; 



s 



■T. » * 













■NT -^, 



tf. v 




<?*. * o N o ' .# 



- 


































Science at a Colliery Disaster 

The illustration shows the rescue party at the Hamstead Colliery disaster preparing to 
descend the shaft. Each member of the party is equipped with an artificial respirating 
apparatus, so that in effect he carries his own atmosphere with him and avoids breathing the 
poisonous gases in the pit. 



THE ROMANCE OF 
MODERN CHEMISTRY 

A DESCRIPTION IN NON-TECHNICAL LANGUAGE 

OF THE DIVERSE AND WONDERFUL WAYS 

IN WHICH CHEMICAL FORCES ARE AT 

WORK. AND OF THEIR MANIFOLD 

APPLICATION IN MODERN LIFE 



BY 



JAMES C. PHILIP, D.Sc, Ph.D. 

KV AT TIIK 1MIER1AI. Cul I EGE OF 
SCIENCE AND TECHNOLOGY, SOUTH Kl 



Wm - 16 DIAGRAMS 



PHILADELPHIA 

J. B. LIPPINCOTT company 

LONDOl . CO. I.l D, 

1909 



By Transfer 
Maritime Co cam, 

SEP 3 **W 



PREFACE 

PROBABLY most people, when they think of 
Chemistry, suppose that its fascination and ita 
practical bearings can be appreciated only by those 
who ha equestered laboratory, the 

door> of which are closed to the uninitiated. This is a 
mistaken vi in countless wonderful ways, unknown 

to the genera] reader, chemical science is supplying the 
ofdinarj and contributing to the conveniences of 

modern lite. 

In the present volume an attempt has been made to 
with this of the subject, and the points of 

1 are different from those of the ordinary text- 
book. Hie author ventures to think that those readers 
who have no technical knowledge may be convinced thai 
am and other things which figure bo largely in the 

ire by no m< ans the only scientific matters of 
thrilling int. <p- even readers who are already 

liar with the elements of the science may be helped 

h the many unsuspected and marvellous * 

in which cln at work beneath our very 

<d that the reader who 



PREFACE 

takes them in order will understand what is brought 
before him much more easily than if he were to pick 
out subjects here and there. Only by such consecutive 
reading is it possible for him to secure the maximum 
of interest and instruction. 



6 



AUTHOR'S NOTE 

Thy. author desires to express his indebtedness to the 
following firms and individuals for the kind help they 
have afforded him in connection with the illustrations of 
this book : Siebe, Gorman, & Co. ; Price's Patent Candle 
Ltd. ; Thermit, Ltd. ; Robertson Electric Lamps, 
Ltd. ; British Aluminium Co. ; Merryweather & Sons, 
Ltd. ; United Alkali Co., Ltd. ; the Director of the 
Deutsehefi Museum, Munich ; Edward R. Bolton, Esq. ; 
Charles Dawson, Esq. ; Oscar Guttmann, Esq., A. D. Hall, 

., F.R.S. ; Sir Frederick Nathan; Dr. J. A. Voelcker. 
He desires also to thank Dr. Frank Clow r es & Messrs. 

In, Lockwood, & Sons, Ltd., for permission to copy 
an illustration for Diagram 8, and Charles T. Heycock, 

. F.R.S., for permission to copy a photomicrograph 
ram 15. 



CONTENTS 

CHAPTER I 

'inn DAWS 01 OB 

FA6I 

y in the ancient world— The metals and the planet >- 
Kule of thumb— -Speculation versus experiment— Fire, air, 
earth, and water 17 

CHAPTER II 

ALCHEMY AM) Till: PHILOBOPHIB'S STONE 

ft v in the 1 -Sulphur and mercury — Tran>- 

mutation of t he metalfl — Apparent conversion of iron into 
copper — Opportunity for quack chemists— Evils of alchemy, 
and how it became a matter of history only . . -1 

CHATTER 111 

nature'? BUILDING material 

table, and mineral— Organic and inorganic— The 
irreducible minimum — Elements, and how they become, 
partners — The difference which chemical forces make — 
Atoms and molecules — Something beyond the power of the 
microscope 

CHAPTER IV 

i) HOW wi; OTOW Of '1HLIK BZI0TBNC1 

Believing without seeing — How we Hydrogen 
and balloons — Tl ndles and mi< 
dang - accommodates it -elf to circum- 
stances — Restless activity where there ifl apparent Stagnation 
—Gas molecule versus express train 

CHAPTEB V 

IS WITH I ITY 

How an element changes its nah, g ttfl name — 

: and charcoal — 
I— The diamond useful as well M DrHf> 
mental — Oxygen and the "smell of eleotrioit; 
molecules which arc the same externally may dinVi in 
anatomy — A carious case of self-effacement in i rystals . 

B 



CONTENTS 

CHAPTER VI 

METALS, COMMON AND UNCOMMON 

PAGE 

An aristocracy among the metals — Gold and platinum — Iron in 
modern life — Cast-iron, wrought-iron, and steel — How razors 
and watch-springs are hardened — Aluminium and its affec- 
tion for oxygen — Thermit — A metal that does not tarnish — 
Platinum in electric lamps— Why we want tantalum now- 
adays 61 

CHAPTER VII 

WHERE TWO METALS ARE BETTER THAN ONE 

Metals not always what they seem — Tinplate, galvanised iron, 
and the common pin — Why a sovereign is not made of pure 
gold — Common solder — Fire-alarms and sprinklers — The 
melting-point of alloys ... .... 72 



CHAPTER VIII 

ACIDS AND ALKALIS 



What an acid is, and how it may be "killed" — Engraving on 
metals — An ink which marks glass — Oil of vitriol and its love 
for water — The chemical fire-engine — Alkalis as antidotes — 
How one may safely enter a poisonous atmosphere — Ammonia 
and lime — Energy manifested in the slaking of lime — Mortar 
the scene of unceasing chemical activity .... 

CHAPTER IX 

NATURAL WATERS, AND WHAT THEY MAY CONTAIN 

How two gases make one liquid — Some physical peculiarities of 
water — Hard and soft water — The making of a lather — 
Carbonate of lime and the "furring" of a kettle — Stalac- 
tites, stalagmites, and petrifying springs — How fresh water 
is obtained from sea water — Germs in water and their 
removal — Seltzer water, Epsom salts, and sulphur springs . 

CHAPTER X 

CHEMICAL CHANGES WHICH PRODUCE LIGHT AND HEAT 

The " Red Flower "—Chemistry of a Candle—The use of a lamp 
chimney — Can smoke be abolished ? — Gas stove versus coal 
fire — The Bunsen burner — The wonderful changes that ac- 
company combustion — Slow burning in the human body — 
How two men are equivalent to one gas burner — Rusting a 
kind of slow combustion 



. 



10 






CONTENTS 

CHAPTEB XI 

now mtl Eg mai>i; 

paoi 

n— Two minutee required bo gel a light— Flint 

steel — Fin ; burning^ he firsl luoifer 

matches — The dangers of phosphorus, and how they are 

a hundred million matches a day in England 

iner's lamp and catalytic action — A modern oigar- 

baneous combustion— Why haystacks and oily 
i take fire of their own accord lis 

CHAPTER XII 
NATURE'S BTOBB8 01 n'EL 

.'—Why burning wood I >re than burn- 

How an American engineer " struck oil" — Bubter- 
Statea and Bussia— Natural 
gas in England — When will it be necessary to carry i 

—Fuel from peat bogs — F( BOuroe of 
fuel 131 

CHAPTEB XIII 

MOBfl ABOUT n 

•nt in the making of coal gas — What happens 

Valuable ; from the gasworks 

•ke for iron-smelting — Water gas — The energy latent in 

a pound of coal — Liquid versus solid fuel — George .Stephenson 

and u bottled-ap sunshine n . . . . . .142 

VPTER XIV 

MB: WHAT IS I L ? 

llnw ail may be 

of a flame— Whi flame 

luminous top of Mont Blanc — Ignition 

nines — Davy'a 

y lamp — How fire-damp is detected by flame-oapa . . 16 1 

AITEU XV 

l 1XPL081 ■ 

sitivc si; ury 

fulm "inflai and 
powders- arder 
— N 166 

ii 



CONTENTS 

CHAPTER XVI 

BELOW ZERO 

PAGE 

Arctic exploration in chemical laboratories — Why salt and ice 
conspire to produce cold — Carbonic acid snow — Liquid air 
obtained by self-cooling — How liquid air is kept — Bacteria 
and seeds at very low temperatures — Liquid hydrogen and 
liquid helium — The absolute zero of temperature . . .180 

CHAPTER XVII 

CHEMISTRY AT HIGH TEMPERATURES 

The distillation of metals — How partnerships are dissolved at 
high temperatures — The oxyhydrogen flame — The electric 
furnace — How sand may be converted into vapour — Calcium 
carbide and acetylene — Nitrogen from the air for agri- 
cultural purposes 193 

CHAPTER XVIII 

CHEMISTRY OF THE STARS 

What is the composition of the sun and the stars ? — Meteorites 
— The marvellous power of the spectroscope — The solar 
spectrum — Elements in the sun — Helium and its story — 
How the spectroscope has led to the discovery of new 
elements — The Aurora Borealis 203 

CHAPTER XIX 

CHEMISTRY AND AGRICULTURE 

The chemistry of vegetable growth — How crops feed — Starch 
and sugar from carbon dioxide — The constituents of meadow 
grass — Nitrogen in the soil, and how it gets there — Assisting 
Nature — Concerning the various kinds of manure — Chili 
saltpetre and sulphate of ammonia — Bone dust and furnace 
slag 215 

CHAPTER XX 

SUGAR AND STARCH 

Foodstuffs and their composition— Carbohydrates, fats, and pro- 
teids— What " sugar" really means — Beet sugar and cane 
sugar — How charcoal is used in purifying sugar— Glucose, 
and where it comes from — Arsenic in beer — Starch converted 
into sugar— Alcohol from cotton rags— Cellulose and cellu- 
loid 227 

12 






CONTEXTS 

CHAPTER XXI 

FATS AND OILS 

PAGE 

The varied sources of fats and oils— Edible fats — Margarine — 
Drying oils in paints and varnishes — Putty and linoleum — 
Oil's as lubricants and illuminants — Tallow dips and snutfers 
— Stearine and paraffin wax in candles— Hard and soft soap 
—Glycerine 887 

CHAPTER XXII 

HOW MAN COMPETES WITH NATURE 

active and constructive work in chemistry — Analysis and 
I — A red-letter day in L828— WflhleVs synthesis of 
urea — How organic substances are built up from inorganic 
materials — How artificial alizarin has ousted the natural dye 
from the market — Natural indigo badly hit — Synthetic 
versus natural camphor — Artificial rubies .... 248 

CHAPTER XXIII 

THE ADULTERATION OF FOOD 

Adulteration no new thing — Common foods not always what 
they seem — Butter and miik— The microscope in the detec- 
tion of adulteration — Preservatives in food— Boric acid, 
formaldehyde, salt, and sugar — Strange composition of 
egg substitute 260 

CHAPTER XXIV 

THE VALUE OF THE BY-PRODUCT 

Rubbish heaps of our modern civilisation — Blast-furnace slag — 
Cement and slag wool— A fertiliser as the by-product of 
manufacture — The wonderful story of the soda industry 
— How refuse has been converted into riches — Alkali waste 
recovery — Where private profit and public interest have been 
served together — Old methods threatened by new discoveries 2G ( J 

CHAPTER XXV 

VALUABLE SUBSTANCES FROM UNLIKELY SOURCES 

The unlovely products of the gas-works, and what is got out of 
them — Undesirable impurities converted into useful materials 
— Sulphur and sulphate of ammonia — Coal tar -Mr. Mackin- 
tosh and waterproof material — V. :ling — Foundation 
of the aniline dye indu :ish darkness— The trail of 
the tar —Lyddite, phenaotine. Mi 



CONTENTS 

CHAPTER XXVI 

CHEMISTRY AND ELECTRICITY 



PAGE 



How chemical changes produce an electric current — Volta's cell 
—The harnessing of chemical energy— Electricity contributes 
to the advance of chemistry— Electrolysis— Sir Humphry 
Davy's experiments— Eefining of copper— How aluminium 
is obtained— A new feature in the Scottish Highlands. . 290 

CHAPTER XXVII 

SOME INTERESTING FACTS ABOUT SOLUTIONS 

Sugar and salt dissolved in water— Solutions the scene of con- 
stant activity — Diffusion and osmosis — Behaviour of blood 
corpuscles in water and salt solutions — Freezing-point and 
boiling-point of solutions — How to get fresh water from salt 
water— Molecular suicide— An interesting procession . . 302 

CHAPTER XXVIII 

FROM SOLUTIONS TO CRYSTALS 

How saltpetre is crystallised — The effect of sowing a super- 
saturated solution — The rate of crystallisation of phosphorus 
— How the formation of crystals is induced by scratching — 
Dry crystals which contain water — Curious changes of colour 
— Sympathetic inks — Crystals in metals, and how they are 
detected — A curious application of the Kontgen rays . . 314 

CHAPTER XXIX 

GREAT EFFECTS FROM SMALL CAUSES 

Significance of small quantities — How a little water makes a 
big difference — How gases are dried — Incandescent mantles 
and luminous paints — Catalytic actions — A revolution in the 
manufacture of sulphuric acid — How hydrogen may be burned 
at the ordinary temperature — Catalytic agents in the human 
body 326 

CHAPTER XXX 

HOW TRIFLING OBSERVATIONS LEAD TO GREAT DISCOVERIES 

How Priestley discovered oxygen— A cut on the finger leads to 
the preparation of blasting gelatine — A cracked glass jar, and 
what it led to — An accident which played a part in the 
manufacture of synthetic indigo — A famous chemist just 
misses an important discovery — The detection of argon — 
The significance of a small difference in weight . . . 335 

u 



LIST OF ILLUSTRATIONS 



\r a Colliery Disaster 

Alchemist's Laboratory 

Molten Iron without \ Furnaci 

Sealing Platinum Wires into an 
Electric Glow Lamp 

A Chemical Fire-Engine 

How a Man may Breathe Safely 
a Poisonous Atmosphere 

A Simple Chemical Change . 

A Wonderful Result of Prolonged 
Chemk al Action 

Where Stalactites Abound . 

A Wonderful Ceiling . 

A Bio Blaze at Baki 

Where it Rains Petroleum . 
a Burning Oil Well 
iural Gas in England 

What Modern HlGH EXPLOSIVE! CAM DO 
IN THE MaNUFACTUR] Of 

Explosive . 

15 



Frontispiece 

To face page v J4« 

64 

TO 
>> >» 82 

m n 88 

96 
100 
104 
HO 
18* 
184 
140 
166 

170 



LIST OF ILLUSTRATIONS 

Working Under Cover . . . To face page 174 

A Dangerous Area . . . . „ „ 178 

Influence of Various Manures on the 

Growth of Wheat . . . ,, „ 216 

1. An Over-dose and its Remedy 

2. The Results of Assisting \ . „ „ 

Nature 

Candle-Moulding on a Large Scale . „ ,, 244 

How the Microscope Reveals Adul- 
teration „ „ 266 

The Rubbish Heap of a Chemical 

Industry „ ,, 278 

A Striking Feature of Modern 

Aluminium Works . . . . ,, „ 300 



16 



THE ROMANCE OF 
MODERN CHEMISTRY 

CHAPTER I 

THE DAWN OF CHEMISTRY 

IN this twentieth century chemistry has become a 
Veritable storehouse of wonder, a cavern of marvel 

ami mystery. Many generations of scientific workers 

have done their share in the exploration of the cavern, 

anil in the discovery of keys to its innumerable chambers, 

but much that is obscure or unknown remains. To-day 

there are more explorers than at any previous time, more 

eager spirits than ever sucking to gain an entrance into 

> chambers which have not yet yielded up their 

1 mil anon some worker, more ingenious or 

rtunate than his fellows, makes a notable advance, 

and his name is on every one's lips. But all the time, 

Unthought of by the outside world, the rank and file of 

the explorers is steadily pushing forward and conquering 

natmv*- mysteries for the ultimate service of man. 

In tin- volume we -hall take a peep into some of the 

chambers which the workers of the past have opened up to 
11 as into some of those which are still partly unex- 

We -hall see how the subtle chemical forces which 

are at work all around us have been revealed and harna i d 

be use of man, and how order ha- been introduced into 

Lpparently hopeless confusion of chemical phenon* 

n 



THE DAWN OF CHEMISTRY 

It is not easy to say definitely where and when man 
first began to grope after the knowledge of chemistry. 
Of all the ancient nations the Egyptians seem to have 
been the most prominent in this respect ; their knowledge, 
however, was not acquired in any systematic way, but was 
rather the result of chance observation. By comparison 
with the store which has been accumulated in the interven- 
ing centuries, the chemical knowledge of the ancients was 
a negligible quantity. They stood merely on the threshold 
of the storehouse, little dreaming of the spacious chambers 
into which succeeding generations were to find their way. 

Suppose we consider for a moment what actually was 
the sort of chemical knowledge possessed by the nations 
of antiquity. They were acquainted with seven metals, 
namely, gold, silver, copper, tin, iron, lead, and quick- 
silver, and although some of these — gold, silver, and copper 
to a smaller extent — are found as such in nature, the 
others would have to be extracted from their ores ; the 
ancients must therefore have been familiar with the 
metallurgical processes necessary for this purpose. It 
was not long before these seven metals became associated 
with the sun, moon, and the then known planets, each 
metal receiving the name and symbol of one heavenly 
body as shown below :— 



Gold 


The Sun 


© 


Silver 


The Moon 


) 


Quicksilver 


Mercury 


? 


Copper . 


Venus . 


? 


Tin. 


Jupiter . 


V 


Iron 


Mars 


6 


Lead 


Saturn . 


h 



This method of representing the metals by symbols sur- 

18 






THE DAWN OF CHEMISTRY 

vived till the Middle Ages, and in old prints one may see 
a flask or bottle within which is sketched a representation 
of the sun. This is to be taken as indicating that the 
Ha>k or bottle contains a solution of gold. 

Besides metallurgical operations the processes of soap 
and glass manufacture, of pottery making, and of dyeing- 
were known and practised in ancient times. Such sub- 
stances as lime, acetic acid, sugar, soda, potash, alum, and 
oil of turpentine were in frequent use. The manufactur- 
ing processes just mentioned are all essentially chemical, 
but they were carried out merely by rule of thumb, and 
not on any scientific plan. This is not to be wondered 
at, for the practical operations were in the hands of 
artisans alone, and it was not the correct thing for the 
philosophers of the ancient world to bring their wisdom to 
bear on arts and crafts. There was in fact a complete 
divorce between the practical and the theoretical, and 
therefore no real science ; the educated people did not 
come into touch with the experimental facts on which 
alone a science could be soundly based. 

The proper sphere of philosophers was considered to 
be speculation pure and simple, and to such purpose 
did they speculate on casual observations that the most 
grotesque theories were evolved, quite out of harmony 
with actual facts. An instance of the sort of thing to 
which this purely speculative science led is furnished by 
an argument of the eminent philosopher Aristotle. As 
a result of >ome of his speculations he came to the con- 
clusion that a vessel filled with ashes would contain as 
much water as one of the same size which has no ashes in 
it. But there was absolutely no desire to see whether 
this was actually the case or not. These philosophers 
in fact stood on the threshold of Nature's storehouse, 

19 



THE DAWN OF CHEMISTRY 

endeavouring to predict what should be found within, but 
never making any attempt to effect an entrance, and see 
how the facts squared with their predictions. 

In one respect, however, the chemical speculations of 
the ancient philosophers demand some attention, and that 
is in regard to the ultimate constituents of the visible 
world. There were supposed to be four primitive inde- 
pendent substances or elements, namely, fire, air, earth, 
and water, by the combination of which in different pro- 
portions the most varied products could be obtained. 
According to Empedocles, for example, flesh and blood 
consist of equal parts of all four elements, while bones are 
one-half fire, one-quarter earth, and one-quarter water. 

The word " element " applied to these primitive inde- 
pendent substances has scarcely the same meaning as that 
which we nowadays attach to it, and indeed Aristotle 
regarded fire, air, earth, and water as the manifestation of 
different properties carried about by one and the same 
kind of matter. The four adjectives "warm," "cold," 
" dry," and " moist," describe the fundamental qualities 
which he supposed to be associated with this primordial 
matter, and to each of the four elements were assigned 
two of these properties. Air was represented as warm 
and moist, water was moist and cold, earth was cold and 
dry, fire was dry and warm. 

All this seems very fantastic, but it was a way of 
looking at things that was current for a long time after 
Aristotle, indeed down to comparatively recent times. 
We may well wonder whether the views which we 
hold about the origin and composition of the natural 
world will be thought equally fantastic by our scientific 
descendants ! 



20 



CHAPTER II 
ALCHEMY AND THE PHILOSOPHER'S STONE 

IN the previous chapter it was suggested that the 
historical development of chemistry has resembled 

the gradual exploration of a cavern full of wonder 
and of treasure. The reader must not suppose, however, 
thai the progress of the exploration has at all times been 

ill v rapid and equally important. On the contrary, 
there have been centuries during which chemists con- 
tributed very little to the real advance of their science, 
simply because their explorations were carried out under 
an entirely false guiding principle. 

This remark applies to the long period in the Middle 

- during which devotion to alchemy was supreme, 
and although the alchemists in the course of what some 
one has called their u potterings m found out many new 
substances, and invented many useful processes, their 
work was singularly unproductive in the interpretation 
of chemical phenomena, and in the discovery of general 
principle-. They missed the spacious chambers in the 
use in their blind adherence to the idea that 
it was possible to convert the baser metals into gold, 

lost their way in subterranean passages where little 

is to be found. 
\\ i that in the nations of antiquity the 

ical and practical sides of natural science were 
separate. TMs state of affair-, so dis- 



THE PHILOSOPHERS STONE 

astrous to the advance of true science, was remedied to 
some extent in the Middle Ages, for the alchemists were 
not only practical experimenters, but also, many of them 
at any rate, men of considerable learning and intellectual 
ability. Unfortunately, however, their chemical theories 
were based on the fantastic views of the ancient philo- 
sophers, and to these theories the alchemists stuck like 
limpets to the rock. They had yet to learn that the 
true method of advance in science is first to study the 
phenomena and collect the facts, and then build up a 
theory ; the alchemists, on the other hand, preferred to 
start with an a priori theory, and then to try to make 
the facts fit into it. 

Curiously enough, the theory of the transmutation of 
the metals, which dominated the chemistry, or rather 
alchemy, of the Middle Ages, came in the first place from 
Arabia. After their conquest of Egypt in the seventh 
century a.d. the Arabians probably absorbed and de- 
veloped such scientific knowledge as was then in existence, 
and in any case the first man, a satisfactory record of 
whose chemical work has come down to us, was an 
Arabian, Geber by name. He had quite a remarkable 
amount of practical chemical knowledge for that early 
time ; many kinds of apparatus, and many laboratory 
operations, such as distillation, filtration, and crystal- 
lisation, which are indispensable to every chemist, were 
familiar to him. 

Valuable as Geber's practical work was, his theories 
about the nature of the metals were very wide of the 
mark. He considered that the metals were all composed 
of sulphur and mercury; these two substances, or two 
principles which were embodied in them, were regarded 
as the "parents" of all the metals. One metal was 

22 



THE PHILOSOPHERS STONE 

supposed to differ from another only in the proportion 
of mercury and sulphur which it contained ; thus gold 
iras particularly rich in mercury, whereas the common 
metals had a large proportion of sulphur. On this view 
it ought to be possible to change one metal into another 
by merely altering the relative proportion of the two 
constituents, and the problem of transmuting lead or 
copper into gold would then be reduced to the discovery 
ome agent which would withdraw sulphur from the 
baser metal and add mercury to it. 

That this way of looking at things should be accepted 
at all is perhaps not so very strange when we consider 
what the thinkers of a thousand years ago had inherited 
from Aristotle and other ancient philosophers. We have 
seen that Aristotle regarded tire, air, earth, and water 
a- different properties carried by one original kind of 
matter, and it is not a very big step from this view to 
the belief that by simply modifying its properties one 
kind of matter could be converted into another kind. 
Since water was regarded as moist and cold, while air 
was moist and warm, it was thought possible by heat 
alone to convert the second chief property of water into 
the second chief property of air ; that is, it was believed 
that water could be transformed into air. 

So we see that the views of Geber and the alchemists 
who followed him in the Middle Ages were more or less 
itural development of the speculations of the ancient 
philosophers. What is difficult to understand is how 
the belief in the transmutation of metals continued to 
dominate the study of chemistry so long as it did, for 
it was not until the beginning of the eighteenth cen- 
tury that chemists became generally sceptical about the 
possibility of converting base metal into gold. For the 



THE PHILOSOPHER'S STONE 

space of eight centuries or thereabout the efforts of the 
great majority of those people who studied chemistry 
were directed to the discovery of the Philosopher's 
Stone — the Great Elixir which should have the power 
of changing lead or any other common metal into the 
noble gold. 

If we are to trust the records that have come down to 
us, the philosopher's stone was not only sought for, but 
found, — by a few favoured individuals. An eminent 
physician and chemist, van Helmont by name, who lived 
in the seventeenth century, states that with a small speci- 
men of the philosopher's stone, received from an unknown 
source, he had transformed a considerable quantity of 
mercury into pure gold. A little later a physician in the 
household of the Prince of Orange published a detailed 
description of the way in which, with the help of a certain 
preparation, he had effected the transmutation of lead 
into gold. 

What are we to make of these stories ? For no single 
chemist nowadays believes that anybody ever succeeded 
in producing so much as one grain of gold from any of 
the baser metals. The two men whose statements about 
the production of gold have just been quoted were 
eminently respectable, and there seems to be no ground 
whatever for supposing that they wished to deceive their 
contemporaries or posterity. The only conclusion to 
which we can come is that they were themselves deceived, 
that they were the victims of illusion. That seems to be 
the most charitable explanation. 

We may, however, ask the question whether there was 
anything at all to account for the transmutation of metals 
being regarded as an incontrovertible fact for so long a 
period. No doubt the ancient tendency to place more 

24 



THE PHILOSOPHERS STONE 

trust in an abstract theory than in any experimental fact- 
had something to do with the persistence of the belief, 
but in addition certain chemical phenomena were known, 
which to a superficial observer would seem to show that 

metal could be converted into another. For example, 
there is the experiment, which any one may repeat, of 
putting a piece of iron, Mich as a steel knife-blade, into a 
solution of blue vitriol or sulphate of copper. However 
>hort a time the iron is left in the blue vitriol solution, 
it comes out exactly like copper, with the same character- 
istic reddish colour. This is a very simple straightforward 

riment, and to the alchemist it admitted of no other 
explanation than that the iron had been converted into 

m r. We know now that no such change takes place : 

copper corner out of the solution and is deposited 

the -urface of the iron, while by way of holding the 

tee even, an equivalent amount of the iron passes 
into solution. 

her circumstances also favoured the postponement 
of tlie day when the truth about the transmutation of 

ds was to be recognised. For one thing, the alchemists 

ived valuable support from princes and rulers who 
in financial difficulties. It was thought distinctly 

th while to have a man about OOUrt who might be 

\o produce gold out of practically nothing, and alche- 
mists were therefore encouraged to continue their search 
for the philosopher's stone, often at considerable expense 

ons. This money aspect of the business, ^ 

ler will easily understand^ led naturally to all sorts 
ack> and charlatans setting up aa alchemists, and lin- 
ing on the credulity or stupidity of princes who n 
in want of moi i 

pun, the air of . which pervaded the alche- 



THE PHILOSOPHER'S STONE 

mists' doings and writings helped to smother the truth. 
Naturally, a man who thought he had discovered the 
philosopher's stone and could turn lead into gold, was 
very careful not to let his secret get abroad, for if every 
one knew the trick, the gold would have no more value 
than the lead out of which it was made. Hence the 
writings of the alchemists are full of the most unintel- 
ligible nonsense that was ever put on paper. Many of 
them profess to describe their method of preparing the 
philosopher's stone, but the description consists of nothing 
but foolish jargon. 

Perhaps the best way to bring home to the reader the 
extraordinary character of the alchemistic writings is to 
quote the following translation from a book on alchemy 
that appeared in 1608. The philosopher's stone is 
supposed to be describing itself : " I am the old dragon 
that is present everywhere on the face of the earth ; I am 
father and mother ; youthful and ancient ; weak and yet 
more strong ; life and death ; visible and invisible ; hard 
and soft ; descending to the earth and ascending to the 
heavens ; most high and most low ; light and heavy ; in 
me, the order of nature is oftentimes inverted, in colour, 
number, weights and measure. ... I am the carbuncle 
of the sun, a most noble clarified earth, by which thou 
mayest turn copper, iron, tin and lead into most pure 
gold." 

The philosopher's stone was supposed to possess the 
most marvellous power, Roger Bacon, one of our own 
countrymen, declaring that it was able to transform a 
million times its weight of base metal into gold. Be- 
sides this it was supposed to have the power of prolong- 
ing life, and was therefore regarded as an "elixir vitae." 
Many other beliefs held at that time were, however, 

26 



THE PHILOSOPHERS STONE 

equally absurd. Thus, for example, it was thought that 
just as an exhausted soil becomes fertile again after a 
time of rest, so a gold mine which was exhausted would, 
if left to itself for a long period, again yield abundance 
of the precious metal ! 

As time went on many chemists, while still adhering to 
their belief in the transmutation of metals, began to work 
on other and more useful lines. One school, headed by 
Paracelsus, devoted themselves to studying the bearing of 
chemistry on medicine, and made a number of valuable 
discoveries in this direction. Faracelsus taught that " the 
object of chemistry is not to make gold, but to prepare 
medicine^," and although this by itself is rather a limited 
Held, it had the effect of gradually drawing men away 
from the pursuit of alchemy. The way was thus prepared 
for the rejection of the alchemistic doctrines, which had 
nig rested like a blight on real chemical science. A 
healthy desire arose to investigate chemical phenomena for 
the sake of knowledge alone, and it was under these con- 
ditions that Nature began to reveal her secrets more 
rapidly. Especially when the explorers discovered the 
i value of the balance and learned what it had to 
teach them about the commonplace phenomena of burn- 
ing, they got back again to the right lines of exploration. 
From that day to this there has been on the whole steady 
progress, and it is now our task to look at some of the 
secret marvels of Nature which have been revealed in these 
last one hundred and fifty years. 



27 



CHAPTER III 
NATURE'S BUILDING MATERIAL 

A COMMON way of classifying natural objects is 
suggested by the familiar questions — " Is it 
animal ? " " Is it vegetable ? " " Is it mineral ? " 
Now, although from the chemical point of view we are 
chiefly concerned with so-called "dead" matter, there 
are many things belonging to the animal and vegetable 
kingdoms which we must take into consideration. A 
certain object may be assigned to one of these two 
kingdoms, not because it is at present alive, but simply 
because at one time or another in its history it has 
been a part of a living thing, a plant or an animal. 
A bone, for example, would be considered to belong 
to the animal kingdom, although in itself it is as dead 
as a door-nail, apart from the living and throbbing 
body of which it was a member. A tree that refuses 
to become green under the touch of spring would still 
be regarded as " vegetable," although, so far as growth 
is concerned, it might as well be a block of granite. 

What makes all the difference between the mineral 
kingdom on the one hand, and the animal and vegetable 
kingdoms on the other hand, is the mysterious thing 
called "life," not the mere materials of which the 
various objects are built up. It is no doubt true that 
the materials associated with plants and animals, and 
thus involved in the processes of life, are frequently of 

28 



NATURES BUILDING MATERIAL 

■ special kind, and this is indicated by describing them 
>f " organic " origin, in contrast to the "inorganic" 

Substances which are more especially characteristic of 
the mineral kingdom. It used to be thought up to 
about one hundred years ago that organic substances 
could be produced only under the influence of life, but 
this has been found to be a mistaken view. The chemist 

produce organic substances in the laboratory, starting 

with inorganic materials, and the organic substances so 

duced are the same in all respects as those formed 

in the living organism. But however much the chemist 

may pride himself on his achievements in building up 

nic substances, there is one thing he has not been 
able to do, and that is to produce an organism, even 

be most elementary kind. Life, which makes all 
the difference between the organic substances and the 

misui, i^ apparently beyond the resources of human 
manufacture. Its origin must be traced to a higher 

A little thought will suffice to remind us of the 

diverse material used in building up our world, both 

organic and inorganic. Besides the coal and the minerals 

which we extract from below the crust, and the many 

things which we grow on the surface of this little island, 

OUT disposal nowadays the products of the 

arth in all their variety. Uul a little 

plification may be introduced into this extraordinary 

diversity when we bear in mind that the chemist has 
. able lo split up most of the complex substances 

with which we are familiar. He has shown that by 

, for example, the action of 

iplex substance may be broken up into simpler 
sub-' latter into ^till simpler one N and 



NATURE'S BUILDING MATERIAL 

on. At last we arrive in this way at an irreducible 
minimum of substances which obstinately refuse to break 
up into anything simpler, and which cannot be converted 
into each other. 

These elements, as the chemist calls them, are, so to 
speak, the bricks out of which all known substances are 
built up. They number about seventy, and each kind of 
brick possesses characteristics which distinguish it from 
all the other kinds. That being so, it is not difficult to 
understand how the combination of the elements leads to 
all the infinite variety of nature. For the reader will see 
at once that if he was provided with seventy kinds of 
bricks, each kind with its own characteristic shade of 
colour, and if he was required to put together a structure 
containing at least two kinds of bricks, and up to any 
number of bricks of each kind, there would be a countless 
host of products. 

Now what are these seventy fundamental substances ? 
Many of them are familiar to the reader, by name at 
least ; for example, lead, sulphur, gold, copper, phos- 
phorus, oxygen, mercury, tin, hydrogen, silver, and carbon. 
But quite half, probably, of the elements are unknown, 
even by name, to the ordinary individual, whilst to the 
chemist himself they are frequently not much more than 
names. And this is not to be wondered at ; for the 
importance of some of the elements, judged by the part 
they play in the building up of the world and in the 
service of man, is extremely small. Thus glucinum, 
gallium, scandium, and many others would not be much 
missed were they to disappear altogether from the family 
of the elements. 

Any one who wants to understand something of the 
fascinating science of chemistry must be quite clear 

30 



NATURE'S BUILDING MATERIAL 

about the part played by the elements and about the 
relations in which they stand to the infinite variety of 
naturally occurring substances. Amongst the elements 
themselves there is great diversity. Some are gaseous 
substances, like oxygen, hydrogen, nitrogen, chlorine, and 
helium ; two are liquids under ordinary conditions, namely, 
mercury and bromine ; while the great majority, chiefly 
metals, are solid substances. But this division of the 
elements into gaseous, liquid, and solid substances is some- 
what arbitrary, and is valid only for the particular con- 
ditions which prevail on our earth. On those heavenly 
bodies which are much hotter than our planet, many of 
the elements with which we are familiar as solids exist in 
the gaseous condition. In the extraordinary heat which 
prevails on the sun even iron is a vapour. 

It must be borne in mind that the elements are found 
in nature mostly in some form of mutual combination. 
Only a few of them occur in the uncombined state, or 
"native" as it is called. The noble metals and some 
other elements, such as copper, sulphur, oxygen, and 
nitrogen, belong to the latter class, but the minerals 
composing the great bulk of the earth's crust are com- 
binations of the other elements with oxygen and sulphur. 
The fact that some elements never occur in the native 
condition becomes intelligible when we make ourselves 
acquainted with the properties of these elements. Take 
the case of phosphorus. The chemist has been able, by 
tin subtle processes, to extract this element from the 
, but it has Mich an aversion to the state 
ingle bles>edne>s, that unless precautions are taken to 
keep it out of contact with air, it reverts to the combined 
e and unites with the oxygen of the atmosphere It 
is therefore easily understood why phosphorus is never 

31 



NATURE'S BUILDING MATERIAL 

found native, and a similar explanation is forthcoming in 
the case of other elements. 

It may occur to the reader to ask — Is it quite certain 
that the so-called elements represent the ultimate units 
of which the natural world is built up ? Is it not possible 
that some substances which are at present regarded as 
elements may turn out to be combinations of other 
elements ? This is perfectly possible, but not very pro- 
bable. It is certainly true that water, soda, and potash, 
which up to one hundred or one hundred and twenty 
years ago were regarded as elements, were then found to 
be really compound substances, and it is conceivable that 
a similar thing might happen again. But it is less likely 
nowadays, for a substance which has to run the gauntlet 
of the chemist's modern methods of attack can scarcely pass 
unscathed unless it is really of an elementary character. 

On the question how far the present accepted list of 
elements is to be regarded as final, the discovery of 
radium has thrown an interesting and somewhat startling 
light. For it appears that radium, although an element 
in the commonly accepted meaning of the word, is under- 
going continuous transformation into other elements, the 
gas, helium, being one of the products of change. The 
idea that one element could be transformed into another 
was cherished by the alchemists, as we have seen, but the 
whole course of chemical progress in the last century was 
against the acceptance of that idea. And just as chemists 
were getting settled in their minds about that important 
question, radium came along and introduced an air of 
uncertainty again into the whole business. If it should 
turn out that one element can actually be converted into 
another, as radium appears to be changed into helium, 
there will be some support given to the hypothesis that the 



NATURE'S BUILDING MATERIAL 

elements are simply modifications of one original parent 
substance. This plausible suggestion was made long ago, 
and has been revived at occasional intervals, but the evid- 
of experiment has so far been against its acceptance. 
In the earlier part of this chapter the elements have 
frequently referred to as existing in a state of com- 
bination, in the form of compound substances. Now a 
compound of two elements is something quite different from 
a mere mixture. The two elements which combine do so 
in a very thorough and intimate fashion, with the result 
that each, as it were, loses its own individuality, and an 
entirely new individual, with other characteristics, is pro- 
duced. The two differently coloured bricks, which we 
suppose to represent the two elements, are not 
Iv laid side by side so that we could lift the one 
away from the other without any trouble, but they are 
I and coalesced in some mysterious manner into one 
brick, different in shape and colour from each of the 
original out-. The only statement we can make 
with certainty about the new brick is that its weight is 
equal to the sum of the weights of the two component 
bricks. 

It i- very interesting to observe that in some cases we 
can -tart with two elements and make either a mixture 
or a compound of them. Two such elements are iron 
sulphur. If the iron is taken in the form of line 
tilings, which are grey in colour, and if these are inti- 
mately mixed by grinding with sulphur, which is yellow, 
'a powder i- obtained which is intermediate in colour 
and yellow. And in this mechanical 
miv Ii component retains its own characteristics 

e not there The particles of iron 

lean be drawn out of the mixture with a magnel ; the 



NATURE'S BUILDING MATERIAL 

particles of sulphur can be dissolved out by using a 
suitable liquid. The reader will therefore see that it is 
a comparatively easy matter to separate the components 
of a mechanical mixture. 

Suppose now that some of the iron-sulphur mixture is 
put in a tube and that the tube is heated by a flame at 
one end. Something of importance obviously takes place, 
for the contents of the tube above the flame begin to glow 
vigorously and are raised to a white heat. Even if the 
tube is no longer heated externally, the flame being re- 
moved, the glowing continues until the zone of incan- 
descence has passed right through from one end of the 
iron-sulphur mixture to the other. This extraordinary 
display of energy is evidence that the iron and sulphur 
are combining chemically, and if the product is examined 
when it has cooled, it will be found that a new substance 
with entirely different properties has indeed been pro- 
duced. There are no iron particles now to be attracted 
by the magnet, and no liquid can be found which will 
extract the sulphur and leave the iron behind. The 
iron and sulphur particles are no longer lying side by 
side ; they have united and coalesced to form a compound 
— sulphide of iron — the properties of which are quite 
different from those of iron and sulphur. Countless 
other illustrations might be cited of the fundamental 
difference between a mere mixture of two elements and 
a chemical compound of the two. A familiar case is 
gunpowder. This is a mechanical mixture of sulphur, 
carbon, and nitre, and it is only when the gunpowder is 
fired that the real chemical process begins. This pro- 
cess results in the production of a number of new sub- 
stances — gases — absolutely different from the original 
constituents of the gunpowder. 

34 



NATURE'S BUILDING MATERIAL 

Apart from the thorough-going change (rf properties 

which accompanies the combination of two dements, 
chemists have discovered some very remarkable facts 

bearing on the proportions by weight in which combina- 
tion takes place. Elements are exceedingly particular as 
to how far they give themselves away, and nothing will 
persuade them to go more than a certain distance in 
meeting the advances of other elements. When iron and 
sulphur combine, they do BO in the proportion of seven 
parts of iron to four parts of sulphur. If a mixture of 
eight ounces of iron with four ounces of sulphur were 
heated, nothing would induce that extra ounce of iron 
to give up its independence and enter the compound. 
And similarly if we took a mixture of seven ounces of 
iron with live ounces of sulphur, the extra ounce of 
sulphur would absolutely refuse to be anything else than 
sulphur. So that elements combine in perfectly definite 
proportions. However or wherever a compound is pro- 
duced, in the laboratory of the chemist or in the laboratory 
of Nature, it invariably consists of the same elements 
united in exactly the same proportions. 

There are cases, indeed, in which two elements unite 

to form more than one compound. Thus there are two 

oxide- of copper, one containing eight parts by weighl of 

copper to two parts by weight of oxygen, and another 

containing eight parts of copper to one of oxygen. 

Observe that the amount of oxygen uniting with eight 

tfl of OOpper must be either one or two ; no compound 

can be tunned containing between one and two parts of 

gen to eight parts of copper. And this is merelv an 

example of what i- alwav- found to be tli< When 

dement combine- with another element to farm more 

than one compound, the amounts of the -econd element 



NATURE'S BUILDING MATERIAL 

which combine with a definite weight of the first element 
are as one to two, or two to three — some simple ratio of 
that sort. 

These remarkable facts about the proportions in which 
the elements combine were discovered soon after the 
balance had become part of the regular equipment of a 
laboratory, and chemists began to cast about for an 
explanation. The result was that they came to regard 
matter as made up of separate particles of extremely 
small size called molecules, which were incapable of 
further division except by chemical means. A fragment 
of iron, if magnified sufficiently, would thus resemble a 
heap of cannon balls, each cannon ball representing a 
molecule. It must be remembered, of course, that this 
is only a theory, a picture, for nobody has ever divided 
matter so finely that further division was impossible ; 
a single separate molecule has never been picked out ; 
indeed, it must be much smaller than anything that has 
ever been seen, even under the most powerful microscope. 

Although the molecule of a substance is the smallest 
particle of that substance which can exist by itself, it is 
possible to break it up by chemical means. The chemist's 
experiments have led him to believe that a molecule 
consists of so-called atoms, sometimes all of one kind, 
sometimes of different kinds. When the atoms in a mole- 
cule are all of the same kind, it is an element which we 
are considering ; when the atoms are of different kinds, it 
is a compound. To separate the atoms which are present 
together in any one molecule, we bring another kind of 
molecule, with different atoms, alongside. In a great 
many cases the atoms will promptly change partners, and 
new molecules — that is, new substances — are produced. 
Suppose, for example, we bring together a molecule AB, 

36 



NATURES BUILDING MATERIAL 

containing one atom A and one atom R, and another 
molecule CD, containing one atom C and one atom D, 
then a chemical reaction will take place resulting in the 
formation of two new molecules AC and RD, or possibly 
AD and BG 

This way of picturing the constitution of matter 
enables us to explain the definite proportions in which 
elements are found to combine. Take the case of copper 
and oxygen, already mentioned. Chemists have come to 
the conclusion that the atom of copper is four times as 
heavy as the atom of oxygen. Now the simplest way in 
which combination could take place would be by one 
atom of copper joining with one atom of oxygen, to form 
one particle or molecule, as it is called, of copper oxide. 
Each molecule, therefore, of copper oxide would contain 
four parts by weight of copper to one part of oxygen, or, 
what is the same thing, eight parts by weight of copper 
to two parts of oxygen. And what has been said of each 
separate molecule may be said also of the mass of copper 
oxide, which is simply the sum total of the myriad 
separate molecules. The proportion of copper to oxygen 
in the mass of copper oxide would be the same as in each 
individual molecule. 

Remembering that the atoms are indivisible, we can 
easily see that the next simplest ways in which copper 
could combine with oxygen would be by two atoms of 
copper joining with one atom of oxygen, or by one atom 
of copper joining with two atoms of oxygen. The atom 
of copper being four times as heavy a- the atom of oxygen, 
the first of these two compounds would contain eight parts 
by weight of copper to one part of oxygen, while the 
second would contain eight parts by weight of copper to 
four parts of oxvgen. As mentioned above, one of these 

37 



NATURES BUILDING MATERIAL 

compounds, the first, has actually been discovered, and it 
is probable that the second also exists. 

With the atomic theory of the constitution of matter, 
therefore, we can explain the very notable simplicity and 
constancy which characterise the manner of combination 
of the elements. 



38 



CHAFTEB IV 

INVISIBLE SUBSTANCES, WD HOW WE 
KNOW OF THEIR EXISTENCE 

* OEEING is believing" is a familiar proverb, but we 

^S must recognise that the saying does not contain 

all the truth about the relation of seeing to 

believing, and that we believe in many things which we 
cannot see. Even in the realm of matter, apart altogether 
from the realm o\' mind, there are .some things the 
existence of which is not directly obvious by the evidence 
of our senses. The chemist, whose business it is to deal 
with all sorts and conditions of matter, knows many sub- 
stance^ — "gases,* he calls them — of which he could not 

— M Hiere I See, smell, touch, taste." A gas may be 
without smell or taste, it may be as intangible as a spirit, 
and a- for seeing it, why, it may be off' and away while 
the observer still thinks he is looking at it. And yet it 
i^ possible to satisfy ourselves by ^ome more or less 
indirect observations that these invisible, odourless, in- 

giMe, and tasteless substances do really exist. The 

least, believes in the existence of gases such as 

fi, nitrogen, and carbon dioxide as firmly 

lieves in the existence of iron, sulphur, turpentine, 

iter. 

It muflrt be observed that the difficulty which is met 

with in tli' * the Gout gases jusl mentioned d<>« * 

or with all gaseous sub Some betray their 



INVISIBLE SUBSTANCES 

presence by their smell ; coal gas, for example, is invisible, 
but fortunately our noses soon warn us when it is out of 
bounds. Other gases, again, are coloured, and we have 
thus direct evidence of their presence. 

But there are several indirect ways in which we may 
convince ourselves that air, oxygen, nitrogen, hydrogen, 
carbon dioxide, and similar elusive substances have a 
material existence. Air is indeed invisible, but from the 
effects which it produces when in motion we may be 
pretty sure as to its material nature. In every case 
where mechanical work is done, we shall find on con- 
sideration that the origin of it lies in the motion of some 
material body ; and the wind, which in its destructive 
mood can lay low a whole forest, can be regularly har- 
nessed to work by the sails of our ships and the arms of 
our windmills. Since work is done by the wind, there 
must be a material body moving, and the material body, 
in this case, is the air. 

A very good reason for regarding air as a material 
substance is based on the fact, to which every reader will 
assent, that two different material bodies cannot occupy 
a given space at the same time. If we are foolish enough 
to run against a stone wall we learn by experience that one 
material body resents the attempt of another material 
body to take its place ; it offers resistance. Now that is 
exactly how the air and other gases behave. If a tumbler 
is inverted in a basin of water, the water does not rise 
and completely fill the tumbler. There is something 
inside which takes up room and so offers resistance to the 
water occupying the same space. Reasoning from our 
general experience of material bodies, we may conclude 
that the invisible something inside the tumbler is certainly 
of a material nature. 

40 



INVISIBLE SUBSTANCES 

Once again — all solid and liquid substances with which 
we are familiar are characterised as light or heavy — in 
other words, they have weight. In this resped also air 

and oth- conform to what is commonly character- 

istic of all material bodies. It is true that, bulk for 
bulk, gases weigh much less than water, or wood, or 
stone, but the difference is only one of degree. One 
simple way of showing that air has weight is to put a 
little water in a gla>s flask, and let it boil vigorously 
until the flask is full of steam. It is then corked tightly 
and removed at once from the source of heat. When the 
flask and its contents have become quite cold, they are 
put on one side of a sensitive balance, sufficient weights 
being put on the other side to keep it level. The cork is 
then removed tor a moment, and it will be observed that 
the side of the balance on which the flask was placed 
goes down at once, showing that the mere opening of the 
fla-k causes it to become heavier. What has happened 
is that the steam which filled the flask when it was hot 
became condensed to water when the flask had cooled, 
thereby leaving room for air to enter as soon as the cork 
removed. It is the entrance of this invisible some- 
thing from the surrounding atmosphere which makes the 
flask heavier. (-ia-es, then, have weight, and are on this 
ground also to be reckoned as material substances. 

A- In- been -aid already, gases an- very light com- 
pared with other substances ; they are matter in a very 
Dilated form. A pint of water is nearly 800 time 

he*?] pint of ail-, and with the gas hydrogen the 

con ; till more marked* For air i- fourteen and a 

half tin ba1 I pint of w$ 

weigh- 11,500 times as mud) a- a pint of hydrogen* It 

may truly be said that a pint of hydrogen is as light as 

41 



INVISIBLE SUBSTANCES 

the proverbial feather, for its weight is only between one 
five-hundredth and one six-hundredth of an ounce. 
Hydrogen is, in fact, the lightest substance known. 

The fact that hydrogen is so much lighter than air is 
of great importance in the manipulation of balloons. In 
order that a balloon may itself rise in the air and carry 
as well a load in its car, it must be filled with something 
which is considerably lighter than air. For this purpose 
hydrogen is the ideal substance, but coal gas, which con- 
tains a good deal of hydrogen, is often employed. Bulk 
for bulk, coal gas is about half as heavy as air. 

We have been comparing air with hydrogen, but it is 
important to bear in mind that whereas hydrogen is an 
element, air is a mixture chiefly of the two elements, 
oxygen and nitrogen, in the proportion of one volume of 
the former to four volumes of the latter. Air is not a 
chemical compound of oxygen and nitrogen, and from 
what has been said already about the essential difference 
between a mechanical mixture and a chemical compound 
of two elements, it will be understood that the properties 
of air are a sort of cross between the properties of oxygen 
and those of nitrogen. Both these gases are without 
colour or smell, but in their chemical behaviour they are 
widely different. Oxygen is a very active element, eager 
to enter into chemical combination with all sorts of 
bodies, and its power of supporting life is simply one 
phase of its activity. Nitrogen, on the other hand, is a 
neutral, sluggish, and inert gas, without any ambitions in 
the direction of chemical union. This being so, it is not 
surprising that air acts like diluted oxygen, the nitrogen, 
as it were, chilling the enthusiasms of the more active gas. 
Many things burn in air — that is, they combine chemically 
with the oxygen which it contains — but the combustion is 

42 



INVISIBLE SUBSTANCES 

much more vigorous when pure, undiluted oxygen is 
supplied The process of respiration is very similar to 
the process of combustion, and it will be remembered 
that in cases of serious illness, and as a last resort, pure 
oxygen is Bometimes supplied to the patient instead of air, 
in order to support for a little longer the flickering flame 
of life. A little chip of wood serves very well to show 

the difference between pure nitrogen, pure oxygen, and 
the air which is a mixture of both. If the chip is set 
slight and is then blown out, it continues to glow in the 
air for some considerable time. When the still glowing 
chip i^ thrust into a jar of pure oxygen it at once bursts 
into flame, whereas if it were thrust into a jar of pure 
nitrogen it would be immediately and completely ex- 
tinguished. So we learn that of the two chief constituents 
of atmospheric air one supports combustion, the other 
s not. 

Beside- oxygen and nitrogen, there are a number of 
other gases in the atmosphere, but only in very small 
amounts. The chief of these are argon, a gas resembling 
nitrogen, to the extent of 9 volumes in 1000 of air, 
i- vapour in varying amount, and carbon dioxide to 
the extent of :5 or 1 volumes in 10,000. The last- 
mentioned gas is being constantly produced by the com- 
bustion of all sorts of fuel, and in the respiration of 
animals. Whereas the air which we take into our lungs 
contains, as has just been said, '0-3 or '01 per cent, of carbon 
dioxide, expired air contains as much as :j to 6 per cent. 
of carbon dioxide and correspondingly less oxygen. 

to say, this oonstanl enormous production of 

.on dioxide does not lead to any increase in the 

amount of that gas in the atmosphere, Ear it is 

onstantly being removed by the instrumentality of 

4:i 



INVISIBLE SUBSTANCES 

the vegetable world. The green leaves of plants, aided 
by sunlight, have the power of decomposing carbon di- 
oxide, liberating the oxygen, and using the carbon for 
their own consumption. In regard, therefore, to the pro- 
duction and consumption of carbon dioxide, the animal 
and vegetable kingdoms are complementary to each other. 

To the ordinary person it may appear rather a difficult 
matter to detect the presence of these odourless, invisible 
gases, but the chemist has discovered ready methods of 
recognising and distinguishing them. The properties of 
each gas have been carefully studied, and in almost 
all cases substances have been found which will behave 
in some characteristic manner when a particular gas is 
present, and remain unaffected when that gas is absent. 
One of these useful substances, employed to test for the 
presence of carbon dioxide, is lime water. When slaked 
lime is shaken with water, a little of it dissolves, the water 
becomes slightly alkaline, and the clear part free from 
sediment is known as lime water. Now when a mixture 
of gases containing carbon dioxide is shaken with lime 
water, or is bubbled through the lime water, the latter 
becomes quite cloudy, owing to the formation of chalk. 
No other gas behaves towards lime water in this peculiar 
manner, so that we are able to obtain visible proof of the 
presence of a gas which is itself quite invisible. 

It is sometimes very necessary to be able to detect the 
presence of carbon dioxide ; for although the gas is not 
actively poisonous, yet it does not support life, and its 
presence in large quantity is very harmful. In all pro- 
cesses of fermentation, as, for example, in the brewing of 
beer, large quantities of carbon dioxide are produced. 
Further, this gas, being considerably heavier than air, has 
a habit of accumulating at the bottom of vessels and 

44 



INVISIBLE SUBSTANCES 

linn; what may be regarded as invisible pools. Hence 
it has occasionally happened that a brewery worker, de- 
scending into one of the large vata for the purpose of 

ck-aning it, has collapsed fatally — practically drowned in 
the carbon dioxide which had collected at the bottom of 
the vat. When a descent has to be made either into a 
brewer's vat, or into an old well, where a similar accumu- 
lation of carbon dioxide may occur, a lighted candle ought 
first to be lowered to the bottom. Should the candle 
continue to burn as brightly as in the open air, no one 
1 hesitate to follow it. If the candle, however, goes 
out. or even gets dim only, it is evidence that there is 
a dangerously large quantity of carbon dioxide present. 

The element carbon combines with oxygen in more than 
one proportion, giving rise not only to carbon dioxide, 
but also to carbon monoxide. This latter substance is a 
colourless and odourless gas, which burns with a blue 
Hame and is intensely poisonous. Any one who watches 
a clear coal lire on a winter evening will notice little 
of blue flame ; these are due to carbon monoxide, 
which readily combines with more oxygen to form carbon 
dioxide. Carbon monoxide has a curious effect on the 
blood — an effect which is directly associated with its 

onoufl properties. It has the power of forming a com- 
pound with the haemoglobin, the colouring matter of the 
blood, and this involves a slight change of tint. By 
-halving up the BUSpected gas with a little blood, and then 
comparing the latter with BOme of the original blood, 
either bv mere inspection or by mean- of a spectroscope, 

may detect quite small quantities of carbon monoxide. 

B line very interesting lie on record in which mice 

have been used to indicate the pi of carboD mon- 

oxide in an atmosphere Small animals, such ai mice, are 



INVISIBLE SUBSTANCES 

affected by this poisonous gas more rapidly than human 
beings, and the behaviour of mice therefore serves to give 
warning of its presence in dangerous proportions. After 
the Snaefell Mine disaster in 1897, for instance, the rescue 
party, headed by Professor Le Neve Foster, descended 
ladder after ladder in the shaft only after a mouse had 
been previously let down to the next lower level. A 
lighted candle also was attached to the cage containing 
the mouse. " By the aid of this testing apparatus,''' says 
Professor Foster in his Report, " it was easily ascertained 
without any risk that the air was not bad as far as the 
115 fathoms level, and that it became poisonous and 
deadly at the 130. The mice showed precisely the same 
symptoms as human beings ; for, if not completely dead 
on arriving at the surface, they had lost all power in 
their legs, whilst pinkness in the snout recalled the pink 
lips of the dead bodies of the unfortunate miners." 

Until recently it was the regular custom to carry a 
couple of white mice on every submarine boat, the object 
being the detection of any carbon monoxide which might 
be produced by imperfect combustion of the gasolene. It 
appears, however, that mice are not sufficiently sensitive 
to small quantities of the gas, and the practice of carry- 
ing them on submarines is now quite rare. 

The question may have occurred to the reader — 
how does it come about that gases, while obeying the 
fundamental laws of matter in many respects, are yet 
so utterly different from the more compact forms of 
matter with which we are acquainted — namely, liquids 
and solids ? It is not only that gases are frequently 
invisible, but they are peculiar also in their ability to 
occupy fully any space that is offered to them. If a 
quantity of gas which fills a ten-gallon gasometer is 

46 



INVISIBLE SUBSTANCES 
transferred to one holding twenty gallons, the gas will 

occupy every corner of the latter. There is, of course, 
of it at any particular point, and its total weight 
remains the same, but its distribution is carried to the 
utmost limits of the containing vessel, however large 
that may be. A moment's thought will show how 
different tin's is from the case of a liquid such as water. 
Ten gallons of water remain ten gallons whether the 
containing cistern holds ten, twenty, or a hundred gallons. 

B8, then, are distinguished from liquids by their re- 
markable expansibility and compressibility. The space 
or volume which a given quantity of gas occupies depends 
altogether on the pressure to which it is subjected, 
and the very simple law has been discovered that the 
volume of a gas diminishes in the same proportion as 
the pressure increases; that is, when the pressure is 
doubled, the volume is halved ; when the pressure is 
trebled, the volume is one-third of what it was origin- 
ally, and so on. 

The volume of a gas is further very sensitive to 

changes of temperature, and it has been found that a 

which occupies ten gallons at 82° Fahrenheit will 

ipy between thirteen and fourteen gallons at 212° 

Fahrenheit, provided the pressure has remained the same. 
This behaviour, again, is quite different from that ex- 
hibited by liquids. Everybody knows that a pint of 
water doe- not become noticeably more bulky when it 
is raised to boiling. As a matter of fact, it does 

expand, but the expansion is too slight to be detected 

by the • 

These striking differences between gases and liquids 
, obvious to our scientific forefathers, Mud 

bey adopted the explanation which 
1, 



INVISIBLE SUBSTANCES 

still holds the field. We first assume the atomic nature 
of matter ; that is, we suppose that if we had a micro- 
scope powerful enough, we should find that an apparently 
continuous and homogeneous piece of matter is really 
discontinuous, consisting ultimately of tiny, separate, and 
distinct specks or molecules, just as what looks like a 
single homogeneous black mound in the distance may 
turn out on closer inspection to be a heap of separate 
cannon balls. Then we suppose further (and this seems 
very unlikely at first) that in the case of a liquid or 
a gas the ultimate particles are in a state of continual 
motion. The particles or molecules of a gas are to be 
pictured as rushing hither and thither at a very high 
speed, constantly colliding with one another and with 
the walls of the containing vessel. The pressure which 
the gas exerts on the walls of the containing vessel — a 
pressure which we may easily measure — is due simply 
to the impacts delivered by the myriads of moving 
molecules. Each molecule, as it comes up to the wall 
of the containing vessel, delivers its blow, and rebounds 
with undiminished speed, to continue its zig-zag course 
among the other molecules. If part of the wall of the 
containing vessel is removed, then the molecules immedi- 
ately rush ahead and occupy whatever space is offered 
to the gas. 

Although the picture just outlined of the conditions 
which prevail in a gas may seem somewhat improbable to 
the reader, it has been found capable of giving an excel- 
lent interpretation of the varied behaviour of gases. But 
that is another story, and would lead us too far. 

The molecules of a gas are very small compared with 
the spaces between them. When it is remembered that 
the molecules in a volume of gas about the size of a 






INVISIBLE SUBSTANCES 

pin head are thirty million times as numerous as the 
human beings on the face of the globe, it will be seen 
that a gas molecule is quite the smallest thing we can 
think of. Not less surprising than the size of the mole- 
cules is the rate at which they move. If it came to 
toe between an express train and a molecule of 
gen, the train would be hopelessly out of it ; for 
the oxygen molecule slips along at the rate of about 
twenty miles a minute. 

Now why should liquids be so different from gases, 
so much more easily visible, so much more tangible, so 
much less changeable in their volume ? The key to 
the difficulty lies in the recognition that in a liquid 
the molecule^ are much closer together than in a gas. 
Just as one heavenly body attracts another, so a mole- 
cule is subject to the attractive force of the surround- 
ing molecules, and it is only because the molecules of 
a gas are relatively so far away from each other that 
tlie attraction may be neglected in this case. In a 
liquid, however, where the molecules, although still 

1 with the power of rapid motion, exert a power- 
ful attraction on each other, it becomes very difficult 
for an individual molecule to escape through the surface 
of the liquid. There is, as it were, a soda] force exerted 
which Beekfl to prevent the individual molecule desert- 
ing the community. Those molecules which attempt 

«• through the surface with a rush and bo evapo- 
rate have to run the gauntlet of the crowded molecules 
around, and most of them are prevented. Thufl it comes 
that a liquid is not at liberty to expand to any extent 

like a g liquid ha- a definite volume, wheree 

like the Vicar of Bray, adapt- itself to -nit the 

ramrtances in quite a remarkable manner. 

49 i) 



CHAPTER V 

ELEMENTS WITH A DOUBLE IDENTITY 

IN the study of chemistry one constantly encounters 
puzzling phenomena, the interpretation of which 
involves much patient labour on the part of the 
investigator. One of these puzzling things is the fact 
that some substances which are undoubtedly elements 
have a way of appearing in different forms according to 
the circumstances under which they are produced. We 
know that an actor plays sometimes one part, sometimes 
another ; but although his get-up differs from time to 
time, it is always the same man underneath. So an 
element may be found masquerading in the garb of 
strange, unwonted properties, which are apt to deceive 
the onlooker, and it is one of the triumphs of chemical 
science that by its penetrating methods it has been able to 
identify a given kind of matter however it may be masked. 
To begin with, it is found that some substances are 
like the chameleon, which can change the colour of its 
skin, or like the mountain hare, whose fur is brown in 
summer and white in winter. Such substances exist in 
two forms of different colour. It is not only in regard to 
colour, however, that the two modifications differ ; their 
other properties are quite distinct also. A good illustra- 
tion of this is furnished by phosphorus, which was referred 
to in a previous chapter as one of the elements which 
occur in nature always in a state of combination, and 

50 






ELEMENTS WITH DOUBLE IDENTITY 

never free. Phosphorus, however, can be extracted from 
bone ash by certain processes, and when prepared in this 

way it is a yellowish-white, waxy solid which can be cut 

with a knife It has to be kept under water, for it' 

ised to the air it combines with the oxygen and is 

gradually converted into a compound of phosphorus and 

gen. 

Phosphorus i*> very easily melted, and it' the water 
under which it is kept is raised to a temperature a little 

above blood heat, the phosphorus becomes a liquid. It 
i til the greatest readiness, and it', instead of 
being melted under water, a piece of phosphorus is heated 
in the air, it will ignite at a temperature very little 
above its melting-point. 

In the dark a lump of phosphorus exhibits a curious 
glow or phosphorescence, which is directly connected 
with the action of the oxygen in the air upon it. From 
what lias been said it will be understood that phosphorus 
o1 dissolved by water, but there is one liquid which 
•Ives large quantities of the element, namely, carbon 
disulphide. On this property a pretty experiment can 
be based, for if a little of the solution of phosphorus in 
carbon disulphide is poured on blotting-paper, the finely- 
divided phosphorus which is left after the evaporation 
of the carbon disulphide takes lire spontaneously. 

dinary phosphorus i^> further extremely poisonous, 
and many C occ urr ed in which children I, 

been poisoned by sucking the ends of matches, in the 
'ion of which phosphorus is used 

ler now draw a mental picture of this 

IXy -olid, easily melted and readily 

set on I id giving a characteristic 

pho in the dark, and put nde b ith 



ELEMENTS WITH DOUBLE IDENTITY 

it the picture of another substance with the following 
different characteristics: — a red powder which cannot 
be melted, which can be heated in the open air to a 
temperature of 450° Fahrenheit without taking fire, which 
does not phosphoresce in the dark, is not poisonous, and 
not soluble in carbon disulphide. 

Nobody looking casually at these two substances would 
dream of regarding them as anything else than quite 
separate and distinct. And yet the fact is they are 
both the same element — phosphorus. The chemist has 
learned how to convert the ordinary yellow phosphorus 
into the red, and how the reverse change of the red 
into the yellow may be effected. Besides, the compounds 
which are prepared from the red variety are exactly the 
same as those obtained from the yellow form, so that 
there is no doubt that phosphorus is an element with 
a double identity. 

How is it that a given element is able to assume 
different characteristics ? How is it that such totally 
distinct properties can be associated with one and the 
same kind of matter ? There are two possible causes 
for this curious phenomenon, and if we build on the 
foundation already laid in a previous chapter, we may be 
able to make the explanation clear. 

It was said there that the smallest particles of a 
substance which can exist by themselves are called mole- 
cules, each of these containing one or more atoms. In 
the case of an element the atoms which go to make up 
the molecule are certainly all of one kind, but a further 
question arises about the number. And the first possible 
cause of the phenomenon that an element exists in two 
absolutely different forms, like red and yellow phosphorus, 
is simply this, that the molecules in the two cases contain 

52 



ELEMENTS WITH DOUBLE IDENTITY 

a different number of atoms. Since we are dealing with 
one and the same element, the atoms in the two cases 

must be the same in kind, but there may be mote of 
them in the one case than in the other. 
There is, however, another possible explanation. We 

must remember that not only are atoms grouped to 
form molecules, but molecules are massed together to 
form the substance as it presents itself to our eves. If 
the hordes of molecules are arranged in regular fashion, 
then we get a crystalline substance ; if they are arranged 
anyhow, we get an amorphous substance — that is, one 
without form. So with phosphorus, the molecules may 
be marshalled differently in the two varieties. 

Of the two explanations which may thus be given for 
the existence of phosphorus in two distinct forms, the 
latter is the more probable. Red or amorphous phos- 
phorus differs from yellow phosphorus, not in having a 
different number of atoms in the molecule, but in that 
the molecules are arranged differently in the two cases. 

A most interesting and more familiar example of an 
clement occurring in different forms is furnished by 
carbon. There are no less than three modification^ of 
this element, two of which at least are as the poles 
asunder in respect of outward appearance and com- 
mercial value. It is indeed difficult to realise that dull, 
amorphous carbon, in the forms of charcoal or lampblack, 
is the same element as the brilliant, flashing diamond. 
Vet so it i- ; while, in addition to these t wo modifications 
irbon, th I third, quite distinct from both, and 

ously known black-lead, or plumbago. 

I little more distinguished-looking than char- 
coal, but is mean and commonplace in comparison with the 

diamond. The three forms of carbon, however, differ not 



ELEMENTS WITH DOUBLE IDENTITY 

only in outward appearance, but in the value we set on 
them and in the uses to which they are put. 

The diamond is very highly prized as a gem, and 
fetches in the market far more than its weight in gold. 
All real diamonds which the reader has ever seen have 
been obtained from natural sources ; and diamond mining 
is a regular form of enterprise. 

Many attempts have been made in recent times to 
manufacture diamonds, reminding one of the efforts of 
alchemists to convert lead into gold. Reflection, how- 
ever, shows that these modern attempts are considerably 
less ambitious. Their aim is, not to change one element 
into another, but to convert one form of a given element 
into another form. The forms of carbon other than the 
diamond are easily obtainable, and the endeavour to 
change some of this plentiful material into a more valu- 
able article is very natural. 

More than that, the attempt to manufacture diamonds 
has been actually successful from the scientific and 
laboratory point of view, although not from a commercial 
standpoint. Moissan, the French chemist, working on 
the idea that diamonds are carbon which has been 
crystallised under great pressure, dissolved amorphous 
carbon in a crucible containing molten iron, heated the 
crucible in the electric furnace, and cooled it suddenly 
by plunging into molten lead. The temperature of 
molten lead is very much lower than that of molten iron, 
so that the outside portions of the latter in the crucible 
solidified immediately. As the iron inside this crust 
gradually solidified, enormous pressure was produced ; for 
iron, like water, expands when it passes from the liquid 
to the solid state. The carbon, therefore, which was 
dissolved in the iron crystallised out under great pressure. 

54 



ELEMENTS WITH DOUBLE IDENTITY 

gments of diamond were obtained in this way, too 
small, however 9 to be of any value as gems. 

Although it 1880 difficult a matter to obtain even very 
small diamonds from charcoal or graphite, the reverse 
change can be quite simply effected. It' a diamond is 
strongly heated it becomes more bulky and is converted 
into something that resembles coke or graphite; thai is, 
it Loses all the special crystalline character to which the 
diamond owes its brilliancy. 

The reader must bear in mind the distinction between 
artificial and imitation diamonds. Such artificial diamonds 
as were made by Ifoissan were the real article, and were 
found to consist of carbon. Imitation diamonds, on the 
other hand, contain no carbon; they consist of a soft, 
heavy flint-glass, known by the curious name of "paste." 
One interesting way of distinguishing real from imitation 
diamond^ is to bring them close to a little radium salt 
in a dark room ; under this stimulus the real diamond 
phosphoresces, but the imitation article makes no re- 
spoi 

The diamond i> not only ornamental ; it has many 
well. One of the most remarkable things 
about it is it> extraordinary hardness, in virtue of which 
it c i D a piece of hardened steel. With a 

n< ni of a diamond fitted in a stem it is possible to 
writ»,« on glass a- with a pen on paper, and with the 
natural edge of a -mall diamond crystal one can make 8 
cut in a glass pi thai the latter can be broken off 

like a piece i d which has been nearly sawn through. 

He hardness of the diamond accounts also for its greal 

fulness in rock-boring tools; with a diamond drill, 
that i-. cylinder round the edge of which is fixed 

of diamond-, the hardest rocks can be gradually 
55 



ELEMENTS WITH DOUBLE IDENTITY 

pierced. In polishing a diamond the only material which 
is of any use is diamond dust ; even emery is too soft to 
touch it. The phrase " diamond cut diamond " has its 
explanation in what has just been said. 

Graphite, or black-lead, as it is commonly called, is 
easily distinguished from the diamond ; it is a greyish 
black substance, crystalline certainly, but soft and soapy 
to the touch. People gave the name of " black-lead " to 
this form of carbon because they were under the mistaken 
impression that it contained lead. The power of graphite 
to give a mark on paper, a property which has found 
application in the manufacture of pencils, is exhibited 
also by metallic lead, hence the really erroneous name of 
" black-lead." 

There are many other ways in which graphite is use- 
fully applied besides the manufacture of pencils. It is 
scarcely affected at all by exposure to great heat, and is 
accordingly made up along with clay into crucibles for 
use at high temperatures. Then it is used to coat iron- 
work — grates, for example — in order to protect it from 
rusting, and at the same time to give it a shiny appear- 
ance. Another curious use to which graphite is put is 
the lubricating of machinery working at a high tempera- 
ture, at which ordinary oil would be unsuitable. 

Whereas diamond and graphite occur naturally, the 
various forms of amorphous carbon are generally ob- 
tained as the products of human operations. Thus wood 
charcoal is got by the partial combustion of wood, lamp- 
black is the product of the imperfect combustion of oil, 
while animal charcoal is obtained by heating bones very 
strongly. Wood charcoal, lampblack, and animal char- 
coal or boneblack all consist of amorphous carbon, and 
are applied in many useful and interesting ways. 

56 






ELEMENTS WITH DOUBLE IDENTITY 

One of the main characteristics of wood charcoal is its 
power of absorbing gases in large quantities, a property 

which render^ it of value in the purification of bad air. 
By passage through charcoal filters sewer gases and other 
noxious emanations may be rendered harmless. Bone- 
black, again, has a remarkable power of removing 
colouring matter from liquids, such as red wine or indigo 
solution ; it 18 accordingly employed very extensively in 
decolourising sugar during the process of refining. Lamp- 
black, on the other hand, is applied for quite different 
purposes. It is useful as an artist's pigment in both oils 
and water colours, and forms the chief ingredient of Indian 
ink and printing ink. 

The uses to which carbon in its various forms may be 
put are, in fact, legion, and in the face of these it is 
necessary to re-emphasise the fact that diamond, black- 
lead, and charcoal are all modifications of this one element. 
The fundamental experiments on which this statement is 
1 were carried out more than a century ago. Before 
this, people were in great doubt about the exact nature 
of the diamond, but it was then shown that, starting 
with a given weight of either diamond, graphite, or char- 
•btained in all three cases the same weight 
of the ga> carbon dioxide, and nothing else besides. 
This experiment proved incontestably that diamond, 
graphite, and charcoal are merely different forms of one 
and the same element. 

The explanation which wafl given for the existence of 
modifications of phosphorus is valid also in the case 

U'bon. Diamond, graphite, and charcoal differ, no! 
in the number of atoms contained in the molecule, but in 
the arrangement of the molecules to form the substance 
n to our e\ 

51 



ELEMENTS WITH DOUBLE IDENTITY 

There is, however, one notable illustration of an element 
existing in two forms which differ in respect of the 
number of atoms in the molecule. That is the common 
element oxygen. The molecule of this gas contains two 
atoms, but under certain circumstances it is possible to 
induce three atoms of oxygen to club together in a mole- 
cule, and then we have ozone. Long before anybody knew 
about this curious substance, a peculiar smell had been 
noticed whenever an electrical machine was at work, and 
people adopted what seemed the simplest explanation and 
regarded it as the " smell of electricity." We now know 
that an electrical discharge, either as a spark from an 
induction coil, or in the shape of lightning, converts some 
of the oxygen in the air into another substance, ozone, 
which is responsible for this peculiar smell. 

To speak of ozone as " another substance " is both right 
and wrong. It is right because, in regard to the pro- 
perties which it possesses, ozone is quite distinct from 
oxygen. In some respects it behaves like intensified 
oxygen, oxidising things which that gas cannot touch. 
An illustration of this is the extraordinary effect which it 
has on mercury. The merest trace of ozone introduced 
into a vessel containing the metal seems to scare it out of 
its usual behaviour ; the bright, lustrous surface becomes 
dull and unresponsive ; instead of moving about freely, it 
sticks to the glass as if it were greased. 

In a second sense it is wrong to speak of ozone as 
"another substance" than oxygen, for they are simply 
two forms of the same element — " allotropic " forms, as 
the chemist calls them. The existence of phosphorus and 
carbon in more than one modification was attributed to a 
different arrangement of the molecules, but such an ex- 
planation could not possibly be correct in the case of 

58 



ELEMENTS WITH DOUBLE IDENTITY 

s like oxygen and none. For, is has been pointed 
out already, the molecules of a gas are rushing hither and 

thither at a high speed, and any definite arrangement of 
these particles is quite out of the question. 

The few cases discussed in this chapter of elements 
existing in more than one form are simply illustrations of 
what ha^ been observed all over the Held of chemistry. 
It i- very frequently found that two compound substai 
with the same chemical composition are quite distinct 
in their outward appearance and general behaviour. In 
some instances the difference is merely one of crystalline 
form, and is to be attributed to a different arrangement 
of the molecules. In other compounds, however, the 
n of the distinction is far more subtle, and is found 
in a different arrangement of the atoms within the mole- 
cule. The story of the way in which chemists have 
di scove red the internal structure and anatomy of the 
molecule is wry fascinating, but it is long and intricate, 
and \NOiild detain us from excursions into interesting 
fields which are dose at hand. 

One other curious phenomenon, however, deserves notice 
here. When a compound exists in two crystalline modi- 
fications, it is very commonly observed that one of the 
IS has but little persistence, and changes into the 
other on the -lightest provocation. Some years ago the 
writer came across an interesting case of this kind. 11 

obtained a substance which crystallised in the form of 

shiny leaflets, but these were no sooner produced than 

they began to change entirely of their own accord, into 

little i. 1 crystals. Hie first form of the 

subsl existed for more than a few 

minutes. 

A host of similar interesting might be quoted, 



ELEMENTS WITH DOUBLE IDENTITY 

but enough perhaps has been said to convince the reader 
that the study of the various forms in which an element 
or compound can exist reveals Nature in very curious 
moods, and brings the chemist into touch with some of 
the most interesting problems of matter. 



60 



CHAPTER VI 
METALS, COMMON AND UNCOMMON 

NO one can fail to notice that metals and alloys play 
a very important part in the economy of modern 
life, It has not always been so in the history of 
the world, for, M as every schoolboy knows," there was a 
time when tools and weapons were made exclusively of 
stone. That primitive stage in man's conquest of nature 
followed by the Bronze Age and the Iron Age, and 
ultimately, when Greece and Rome were at the height of 
their glory, as many as seven metals were known and 
utilised. At the present time the number of known 
metals is very much greater, and innumerable alloys, 
made by mixing two or more metals, find application in 
our technical and social life. We see them everywhere, 
from powerful engines and gigantic bridges down to 
DeedBea and pins ; we carry them about with us, on our 
boots, in our pockets, on our lingers, in our hail*, and 
Bometimei even in our mouths. 

The majority of tl. 'y known elements are natal-, 

and among these there are all sort- and conditions. Only 
one is a liquid — mercury or quicksilver — and its curious 
.filiation of the pr op er ti es of a metal find those of a 
liquid render it useful for many Special purposes. In the 
^ame way, however, as liquid Water may be converted into 
steam bv heating and into ice by cooling, so the liquid metal 
. be boiled, producing mercm \ \apour. or it mav be 

Gl 



METALS, COMMON AND UNCOMMON 

solidified by the application of cold. Indeed, during winter 
in extremely cold countries like Siberia the mercury in the 
bulbs of the thermometers may be frozen ; this happens 
when the temperature falls 40° below zero Fahrenheit. 

Metals exhibit great variety of density, and it must 
not be supposed that a metal is necessarily a heavy sub- 
stance. It is true that mercury is nearly fourteen times as 
heavy as water, and that gold is about nineteen times as 
heavy, yet there are metals — sodium, for instance — which 
are lighter than water ; if a piece of this metal is thrown 
on water it swims about on the surface. The reader may 
remember aluminium as a comparatively light metal, the 
weight of which, bulk for bulk, is only one-seventh of 
that of gold. 

Only a few of the metals are found in the uncombined 
or " native " condition. These are the so-called " noble " 
metals — gold, platinum, &c. — which are distinguished by 
the fact that they do not tarnish, and are not readily 
attacked by acids. Other metals occur in the form of 
ores, and have to be extracted from these by laborious 
processes. However it has come about, the majority of 
the metals have combined with oxygen or sulphur, and 
their ores consist therefore mainly of oxides or sulphides, 
mixed naturally with a smaller or greater amount of 
earthy matter. The operations or metallurgical processes 
necessary for winning metals from their ores are modified 
by the idiosyncrasies of the particular metal which is 
sought, but the essential chemical reaction involved is 
generally the removal of oxygen from the ore by the 
agency of carbon. If the ore does not already consist of 
the oxide, the latter is obtained by roasting the sulphide 
in a current of air, by which process the sulphur in the 
sulphide is replaced by oxygen. 

62 



METALS. COMMON AND UNCOMMON 

The oxide is mixed with coke, which contains a high 
proportion of carhon and the mixture IS heated in a 
furnace, a "flux," such AS lime, being added to remove 
the earthy matter from the ore in a fluid form. At the 
high temperature of the furnace the carbon in the coke 
deprives the metal of its oxygen and carries it off in the 
form of carhon monoxide or carbon dioxide. The metal 
is thus obtained in the free state, and is generally run out 
of the furnace in a molten condition, while the earthy 
material that was in the ore is separated along with the 
flux as slag. 

Perhaps the commonest example of such a metallurgical 
ration is iron-smelting, a process which may be seen 
at work in many parts of Great Britain. In the case of 
iron it is desirable to inform ourselves a little more about 
what is done with the crude metal obtained from the 
blast furnace, and it is well that we should understand 
the chemical differences between the various kinds of iron 
which are of technical importance, namely, cast-iron, 
wrought-iron, and steeL The different properties which 
characterise these varieties of the metal show in a very 
interesting manner how the behaviour of a pure substance 

i- modified by the presence of small quantities of foreign 
mat • 

Iii a description, given in an earlier chapter, of the 

mpts which have been made to manufacture diamonds, 

it was -aid that molten iron dissolve- carbon. Since now 
in the { of iltm-smelting the fused metal has been 

in contact with coke in the furnace, it is not surprising 
that the crude metal which is taken out of the furnace 

mount of carbon, a- much SS 

ent, : it is run into moulds, mid is then known 

U OIL I tfefill I .inination ha- shown that 



METALS, COMMON AND UNCOMMON 

of the total carbon present in cast-iron some has combined 
with the metal to form a compound known as a carbide, 
while the rest has crystallised out during cooling in the 
form of graphite. 

If the carbon is removed from cast-iron as com- 
pletely as possible we get wrought-iron, which contains 
only about one-tenth of 1 per cent, of carbon, and differs 
very notably in its properties from cast-iron. In the 
first place, wrought-iron can be welded — that is, if two 
pieces of this material are made red-hot they soften, 
and in this state may be hammered together. This 
cannot be done with cast-iron, which is a hard, brittle, 
crystalline substance. 

Again, cast-iron is much more easily melted than 
wrought-iron. The latter is very nearly pure metal, 
whereas the former contains an appreciable quantity of 
foreign material. Now it is a well-known fact that if 
a small quantity of a foreign body is added to a pure 
substance, the melting-point of the mixture is lower 
than that of the pure substance. Salt water, for example, 
contains much more dissolved matter than fresh water, 
and is more difficult to freeze ; or, to put it the other 
way round, ice melts at a lower temperature in salt 
water than it does in fresh ; in fact, a strong solution 
of common salt in water will not freeze even at 0° 
Fahrenheit. The fact that cast-iron melts more easily 
or has a lower freezing-point than wrought-iron is 
therefore an illustration of a very general principle. 
The reader will observe that the freezing and melting- 
points are to be regarded as the same temperature, and 
this is always so if we are dealing with a pure sub- 
stance. The difference is merely this, that if we are 
thinking of the solid being converted into liquid, the 

64 




. WlTHOtn a lr 
The crucihlr ■■-.-. iic alumir . 



"thermit, " and I he mixture ]% 
formation of metallic iron and a 
the iron u d e 

tram rails. The heat of the che 
to be protected by darkened gl 



i en in, whi in the 

I be n olten i 



METALS, COMMON AND UNCOMMON 

temperature at which tin's takes place is called the 
melting-point; if, on the other hand, we are thinking 

of the change of liquid into solid, the temperature at 
which this change occurs is called the freezing-point. 
The two temperatures are the same if the substance 
is pure. 

The third variety of iron, namely, steel, is intermedi- 
ate betwttn cast and wrought-iron in regard to the 
amount of carbon which it contains. The remarkable 
tiling about steel is that when it is heated and then 
suddenly cooled by plunging into cold water it becomes 
exceedingly hard, so much so that it has the power of 
scratching ghass. Curiously enough, if this hard steel 

gain heated and then allowed to cool slozclt/, if is 
found to be nearly as soft as ordinary iron. By re- 
gulating the temperature to which the hardened steel 

Cposed the second time, any required degree of 
hardness may be attained. Articles made of steel, such 

aaon, scissors, and watch-springs, are therefore first 
hardened, and then "tempered' 1 by heating them to a 
point between 4'30° and 560° Fahrenheit, the tempera- 
ture varying according to the purpose for which the 
article i- to be used. A razor, tor example, is heated 

only to 180°, a temperature at which the metal acquires 
superficially a pale yellow colour, due to the forma- 
tion of a film of oxide. Watch-springs or SWOrd-blft 
•In- Other hand, which should be -otter and more 

dasti '1 by heating to 550 . and the colour 

of the surface film p,t-<- through various -hades — 
OW, brown, purple, and blue — as the temperature 
Tin of heal attained in femperi 

the colour of the surface. Thiu 
hard trhicfa I tted to • id thi n 

l 



METALS, COMMON AND UNCOMMON 

allowed to cool slowly, is said to be " tempered to the 
yellow," and is hard enough to take a fine cutting edge. 
It must be remembered that steel which has been 
hardened without being tempered is of no use for 
ordinary purposes ; it is too brittle. 

It is many centuries now since man first began to 
discover the valuable properties of iron, and the passage 
of time has only led to a gradually widened range of 
application, and to improved methods of production. 
One can name metals, however, which for a long time 
after their discovery were regarded as curiosities, and 
have only recently and more or less suddenly been in 
large demand as their useful properties have been 
realised. Aluminium is a notable example of this. Fifty 
or sixty years ago it cost twenty shillings an ounce ; 
now it can be purchased for less than a shilling a 
pound. The very high price of the metal was due, not 
to scarcity of material from which aluminium could be 
produced, but to the fact that there was little or no 
demand for it, and no satisfactory method of extract- 
ing it from its ores. 

As a matter of fact, aluminium is one of the most 
common constituents of the earth's crust, occurring in 
the combined state as mica, felspar, clay, and slate. It is 
in many respects a remarkable metal. It is exceedingly 
light, and yet, unlike most other metals of this class, is 
not easily tarnished even in the presence of moisture. On 
account of its lightness it is extensively used in military 
fittings, while its resistance to the action of animal and 
vegetable juices renders it serviceable in the manufacture 
of cooking utensils. 

Although aluminium in the mass is not easily oxidised 
in air, probably because it gets coated with a thin film of 

66 



METALS. COMMON AND UNCOMMON 

OZlde which actfl as B protective layer, the powdered 

metal burns vigorously , like magnesium! when it is healed, 
and in this way a very high temperature is produced If 
the oxygen which is D ecennar y for the combustion of the 

aluminium is mixed with the metal at the start, instead 

of coming from the air as the burning proceed . an even 
higher temperature can he reached. Bui how, the reader 

may ask, can we mix a gas with a solid ? In the literal 
ertaitlly, this cannot he done, for to burn halt' an 
ounce of aluminium powder as much as fifteen pints of 
would be required But the oxygen may be 
mixed with the aluminium in a compact or condei 
condition in the form of some compound, out of which the 
aluminium has no difficulty in extracting it. 

Iron oxide is such a compound, BO if a mixture of 
powdered aluminium and iron oxide, known as " thermit/ 1 

nited at one point an action sets in which spn 

through the whole mass, giving out intense heat, and 

.ting in the formation of aluminium oxide and molten 

metallic iron. The aluminium, in fact, feeds on the 

gen of which it has deprived the iron. The heat 

'need in this competition for the oxygen is so intei 

thermit mixture is placed on an iron [date 

half an inch thick, and ignited, a hole i- melted in the 

e beat stored up in thermil may, however, be turned 
• practii ounl in the following interesting 

— If the ends of two steel rails are pressed to- 
the intensely hot fluid iron produced 

in tl ion i- run out of a crucible on to the 

junction, tl: ire filled, the beat i such that the 

the 

applied | I that a sound joint i made hi v » 

67 



METALS, COMMON AND UNCOMMON 

similar way thermit may be employed for repairing iron 
shafts and pipes. 

In aluminium we have an example of a metal the price 
of which has fallen in a remarkable manner, not because 
fresh sources of the metal have been discovered, but 
because the increased demand has led to cheaper and 
more efficient methods of production. There are other 
metals, however, which are costly, not because there is 
any difficulty about their extraction, but because the 
natural supply is limited. 

Platinum is a case in point. Endowed with unique 
and valuable properties, it is comparatively rare, and 
possibly the reader has never seen a specimen ; it costs 
nearly twice as much as gold. Platinum is a silvery 
metal, twenty-one times as heavy as water, bulk for bulk, 
and does not rust or tarnish. Like gold, it is a " noble " 
metal, and is not dissolved by any single acid which we 
know, not even by aqua forth (nitric acid). A mixture 
of nitric and hydrochloric acids, however, will dissolve 
both platinum and gold, and it was the power of this 
mixture to attack the latter metal which led the alchemists 
to speak of it as "aqua regia" 

Platinum is in a special sense the chemist's metal. Its 
very high melting-point — 3200° Fahrenheit — and its 
chemical inertness make it valuable to him, and platinum 
crucibles are to be reckoned among the indispensables of a 
properly-equipped chemical laboratory. 

There is another characteristic of platinum which to 
the casual reader may seem most insignificant, but which, 
as it turns out, is of the greatest importance in a certain 
manufacture. This is the fact that with rising tem- 
perature platinum expands at nearly the same rate as 
glass. Why should that be of any consequence ? the 

68 



METALS, COMMON AND UNCOMMON 

reader may ask, and what has platinum got to do with 
gla- Well, it is generally recognised that bodies 

expand when heated — they become more bulky as the 
temperature rises. As a rule, the expansion differs with 
different substances, but it >o happens that platinum 
expand^ to the same extent as glass for a given rise of 
temperature. 

We may realise the significance of this fact when we 
remember that it is sometimes necessary to pass a metal 
wire through the walls of a glass vessel This ha- to 
be done, for example, in the electric glow lamp, the 
illuminating power of which IS due to a carbon filament 
raised to a white heat by the passage of an electric 
current. As the carbon would soon burn away if it 
were surrounded by air, the little glass globe which 
protects the filament must be freed from air and then 
sealed up. The wires, therefore, which carry the current 
must pass through the walls of the globe, and the 
4 ion at once arises, what metal should be used for 
wires ? 

Copper, the metal which is so commonly used for 
electric wiring, would be quite unsuitable, because ii 
l not expand and contract with change of tempera- 
ture at the same rate as glass. If W( passed a copper 
wire through a piece of glass while the latter is hoi and 
soft, and melted the glass all round the wire, then on 
cooling, o^ing to the Unequal contraction of the metal 
and the glass, a condition of strain would be produced, 
ling finally to the fracture of the gL 

A metal js required which expands and contracts at 

ud the one metal with this 

characteristic i- platinum. Hence it OODMS thai an 
electric glow lamp ha> two little pieces of platinum 



METALS, COMMON AND UNCOMMON 

connecting the ends of the filament inside with the 
terminals outside. 

Thus it is that what may seem at first to be nothing 
more than a dry laboratory fact, without any practical 
bearing, may turn out to be of the greatest importance 
for the requirements of everyday life. 

Such a case of the discovery of a new use for a metal, 
and a consequent fresh demand for it, might be paralleled 
by what has happened recently in connection with 
tantalum. This is a rare metal, and up to within a 
year or two ago very little attention had been paid to 
it, as a glance at any chemical text-book will show. 
It has been discovered, however, that tantalum has 
certain properties of commeixual value, and people are 
now on the look-out for fresh sources of this somewhat 
scarce material. 

The illuminating power of the electric" glow lamp 
depends, as has been said already, on a carbon filament 
being raised to incandescence by an electric current. 
Now these carbon filaments are very fragile creations, 
and one might at first be inclined to wonder why fine 
metallic wires are not used instead ; for it is well known 
that a metallic wire is similarly heated by the passage 
of a current. The explanation is simple ; in order to 
get a respectable light from an incandescent metal wire, 
we should have to raise it to a temperature at which 
it would melt. This would happen even with platinum, 
for the temperature of the carbon filament in an electric 
glow lamp is several hundred degrees higher than the 
melting-point of that metal. 

It is just here that the valuable properties of tantalum 
come in. Briefly stated, they are these : tantalum can 
be drawn into very fine wire, about one-thousandth of 

70 




■ ■ 

Sea I.wii- 

=> on heating and contraction cooling at the 
the wires are sealed into the fu t is still ii h> afier cool- 

ing, and the glass is not strained a* it would he if thr 



METALS, COMMON AND UNCOMMON 

an inch in diameter, and itfl melting-point is exceedingly 

high, so high that the tine wire may be raised to a white 
heat by an electric current without melting. 

The tantalum lamp, then, which i- now on the market, 
i- exactly analogous to the electric glow lamp, except 
that the filament i- made of tantalum instead of carbon. 
iency, the tantalum lamp compares favour- 
ibly with the ordinary glow lamp, and it i- said to have 
a longer lite. So the time may come, if sufficient 
tantalum can he procured, when the carbon filament 
will ha\ ue merely a curiosity. 

Tung-ten and osmium are other out-of-the-way metal 
which have recently found an important application in the 
manufacture of electric lamps, BO that tantalum i> not the 
only competitor in the field against the carbon filament. 

The application of electricity to all sorts of obj<_ 
ha- led to extended demands for other metals than those 
just quoted. Copper, for instance, which offers very 
-light resistance to the passage of a current, is much 
in demand for electric wiring; enormous quantities of 
the metal are now devoted to this purpose. Copper 
enter- al-o into the composition of many alloy- — brass, 
bronze, and the like ; but the subject of alloy- i- a big 
and must be reserved for another chapter. 



CHAPTER VII 

WHERE TWO METALS ARE BETTER THAN ONE 

IN the foregoing chapter we have had illustrations of 
the differences exhibited by metals in regard to 
specific gravity and fusibility, but there are, of course, 
many other properties — hardness, malleability, ductility, 
and the like — which have to be taken into account when 
we are considering the suitability of a given metal for 
a certain purpose. Frequently it happens that the metal 
is suitable for the purpose in all respects save one, in 
which case it may be possible to correct the deficiency 
by adding another metal, provided at the same time that 
this second constituent does not detract from the valuable 
properties of the first. The effect of the presence of 
carbon in iron might be considered as an illustration of 
this principle, but carbon is not a metal, and the amount 
present is not great, so that wrought-iron, cast-iron, and 
steel are rather in a class by themselves. 

We may make good the deficiencies of a metal by the 
addition of another in more than one way. It is not 
always necessary actually to mix th^ metals ; we may 
put one on the top of the other, as in tinplate or 
galvanised iron. In regard to strength, durability, and 
cheapness, iron is an excellent material, but the weak 
feature about it is its liability to corrode when exposed 
to a moist atmosphere : it rusts. 

Articles made of iron which have to be exposed to air 

72 



TWO METALS BETTER THAN ONE 

and moisture must therefore be protected. In the ease 
of large structures, such as bridges, Locomotives, and 
steamers, this is done by painting them, but with smaller 

and more easily-handled articles the same end is attained 
by coating them with a layer of another metal which is 
not easily corroded by the action of moist air. Tin and 
zinc are metals which fulfil these conditions, and they 
arc further comparatively fusible, so that a sheet of iron 
dly coated with either by simply dipping it 
into a bath of the fused metal. Iron coated in this way 
with a layer of tin is known as tinplate; similarly 
treated with zinc, it i^ known as galvanised iron. 

So that things are not always what they seem. Even 
the common pin i» a fraud in this sense, for if we could 

i it out we should find brass wire in the inside, quite 
different from the white metal on the outside. Brass, 
as the reader probably knows, is a yellow alloy containing 

• of copper, and the easiest way of showing that pins 
contain this metal is to dissolve one in nitric acid. The 
pin lually consumed by the acid, it ultimately 

disappears, and a blue liquid remains, similar to what is 
obtained by treating a piece of pure copper in the same 
So ire may conclude that there is copper in the 
pin. The white outside is a coating of tin; this, how- 

. i- not put on, as in tinplate, by dipping in a bath of 

letal, but by another interesting method 

e reader may recollect that among the things thai 
lent support to the alchemists' belief il] the transmutation 

he observation thai ;< piece of iron fai- 
led in a solution containing oopper acquires the 
app< This little trick can be perfo rm ed 

with other metals also, and i- applied in the manufacture 
... The brass, wires which form Ll 'the 






TWO METALS BETTER THAN ONE 

pins are put in a solution containing tin, and the result 
is that a coating of this metal is deposited on the brass. 

Such a method of depositing one metal on another 
is very closely related to the process of electro-plating. 
When an electric current is passed between two metal 
rods or electrodes immersed in a salt solution, the salt is 
decomposed and the metallic constituent is deposited on 
one of the electrodes. Suppose now that the solution 
contains a salt of silver, and that we replace the rod on 
which the metallic constituent is deposited by a spoon 
made of some alloy, then on passing the current the 
usual thing happens, and we get a fine, coherent deposit 
of silver on the spoon ; the latter is electro-plated. 

In this way articles made of common metals or alloys 
may be plated with gold, silver, copper, or nickel. For 
example, we can protect steel articles, such as bicycle 
fittings, from atmospheric corrosion by plating them with 
nickel. Articles, on the other hand, which are to be used 
for the table or for ornament may be similarly coated 
with silver. Spoons and forks, for instance, are generally 
made of Britannia metal, an alloy containing mostly tin 
and antimony, or of German -silver, an alloy of copper, 
zinc, and nickel ; when these articles are coated with 
silver they are less easily attacked by acid liquids, and at 
the same time their appearance is improved. 

Plating, after all, is a device for hiding the short- 
comings of one metal by covering it with another. There 
is, however, a second way of making good the deficiencies 
of a metal, and that is by mixing it thoroughly with another 
of different character. In what way the properties of one 
metal are modified by thus alloying it with a second may 
be best understood from a few examples. 

The ubiquitous penny piece is commonly known as "a 

74 



TWO METALS BETTER THAN ONE 

copper.** This metal in the pure condition, however, would 
be too soft for the wear and tear which a coin has to 
undergo, and consequently 5 per cent, of foreign metal 

■<tly tin) is added to the pure copper in order to 
harden it. The curious tiling is that tin itself is quite a 
W& metal, and yet the addition of 5 per cent, of it to 
pure copper produces an alloy which is much harder than 
eopper itself. 

Similarly, pure gold and silver are too soft to be used 
either for coins or ornaments, and for this purpose they 
must be hardened by the addition of another metal, 
rally copper. The colour of an English silver coin 
does not betray the presence of copper, but if a three- 
penny bit were dissolved in nitric acid we should get the 
blue solution which is characteristic of copper. Since 
pure silver dissolved in nitric acid gives a colourless 
solution, we may conclude that our silver coins contain 
copper ; as a matter of fact, they have Ik per cent, of 
that metal. 

An English gold coin is also alloyed with copper to 
the extent of 1 part for every 1 1 parts of gold. Such an 
alloy is described as S3 carat gold, because out of 24 parts 
of the alloy, 9St parts are pure gold. For ornaments 

other alloys are made containing less of the preciou l 

metal, and described OB 18, 12, or B carat gold, these 

eating that 84 parts of the alloy contain 18, 

. or parts of pure gold respectively. 

Another property which IS alteied by adding a second 

metal is the fusibility, and an alloy as a rule meltfl 

much lower temperature than one would expect from the 
melting-point- of the constituenl metals. The inftui 

of I jj : body on the melting-point of I pure 

llready been 1 to in connection with oast 

7fi 



TWO METALS BETTER THAN ONE 

and wrought-iron, but with alloys the effects are much 
more striking. 

Common solder is a case in point. Soldering consists 
in joining two metals by an alloy which is more easily 
melted than either, and which at the same time will 
coalesce with each metal. Tin and lead, a mixture of 
which forms ordinary plumber's solder, melt at 440° and 
617° Fahrenheit respectively, while the solder itself melts 
at 374°. 

The reader may already have remarked the frequency 
with which tin is used either to plate or alloy with other 
metals, and it is in fact very seldom employed by itself. 
Even the so-called " tin " foil in which chocolates are 
wrapped contains lead, and the utensils which we call 
" tins " are generally iron plated with tin. 

In the case of solder, as we have seen, the alloy melts 
at a temperature lower than the melting-point of either 
constituent. But of the lowering of melting-point pro- 
duced by mixing far more striking examples are obtained 
when we take four metals to make an alloy. Lead, tin, 
bismuth, and cadmium melt at 617°, 440°, 514°, and 608° 
respectively, and yet by mixing these metals in certain 
proportions we can prepare an alloy which melts in hot 
water and is known as " fusible metal. " 

These easily-melted alloys are put to some curious uses ; 
for example, in connection with fire-alarms. A quantity 
of fusible metal is arranged in a receptacle in such a way 
that when a certain temperature has been exceeded the 
alloy melts, and releases a spring or allows a lever to 
fall. By this device an electric circuit is closed and a bell 
is rung. 

Then, again, fusible alloys play a useful part in the 
sprinklers which are fitted up in factories and workshops. 

76 



TWO METALS BETTER THAN ONE 

These consist of water-pipes led round the upper part of 
I room, and at intervals on the pipes there arc valves 
secured by fusible alloy. If a fire should break out in 
any room fitted with such a sprinkler, the heat will melt 
the fusible alloy at one or more of the valves, the water 
will burst out, and their U a fair chance that the tire 
will be extinguished before it has attained very large 
proportions. 

With such examples before US of the way in which the 
hardness and fusibility of a metal are altered by the 
addition of another, we are led up to the question — Are 
these alterations due to the formation of a new substance, 

impound of the metals, or are they accounted for by 
the mere mixture of the constituents? 

The difference between a mechanical mixture of two 
elements and the compound formed by their chemical 
combination has already been discussed. We must next 
try to decide whether the features which we generally 
notice in chemical action are to be observed when we 
make two metals into an alloy. Now it must be ad- 
mitted that it is rather difficult to settle the question 
whether an alloy is a mixture or a compound. In some 

acts, it i- true that the mixing of two metals re- 

irhal takes place when two elements combine. 

Thus we hs that when iron and sulphur act on 

i other an enormous amount of heat is liberated, 

and >uch liberation of heat very frequently accompanies 

J action. Well, a similar thing occurs when we 

add sodium to merCUiy to make- an alloy (or an "amal- 
gam, i- called when mercury LB one constituent) ; 
addition of sodium IS accompanied by a flash of 
light. So also when I of aluminium i add* d to 
1 gold, an extraordinary evolution of heal il ob 

Tl 



TWO METALS BETTER THAN ONE 

and the molten mass is raised to incandescence. Such an 
occurrence may be taken as evidence that chemical com- 
bination has taken place. 

Again, the colour of some alloys is markedly different 
from that of the constituents. Silver and zinc are 
both white metals, and yet they form a beautiful pink 
alloy. Gold and aluminium also furnish us with an 
illustration, for when they are mixed in certain pro- 
portions a brilliant purple alloy is obtained, quite dis- 
tinct in colour from both constituents. 

In spite of these examples, however, it must be said 
that we do not observe in the formation of alloys 
generally such a thorough-going change of properties 
as commonly results from chemical combination. The 
question, therefore, of mechanical mixture v. chemical 
compound is not so easily decided. 

Modern investigators have tackled the problem by 
studying the freezing-points of alloys in their relation 
to the freezing-points of the constituent metals, and in 
the course of these investigations many interesting results 
have been brought to light. It is almost the invari- 
able rule that when a little of a metal B is added to 
a metal A, the fused alloy begins to solidify at a lower 
temperature than pure A ; it is said to have a lower 
freezing-point. As we go on adding more and more 
of the metal B, the alloys produced have lower and 
lower freezing-points. The same series of phenomena 
is observed when we add increasing quantities of the 
metal A to the pure metal B. 

Suppose we try to picture these results graphically, 
that is, with the help of a curve. In doing this we 
represent the composition of the alloy by distances 
measured along a horizontal line, while the tempera- 

78 



TWO METALS BETTEE THAN ONE 

tares at which the alloys freeze are represented by 
lengths measured vertically. Tin's is a very common 
method of summarising the results of scientific investi- 
gation and of showing the way iii which one quantity 
depends on or varies with another. An example of 
such a use of curves is furnished by the card which 
Comes off an aneroid barometer at the end of a week. 
On this card vertical distances represent the height of 











/cO^B /(XjXa 



Cam/iosil 

Fir;. }l. 






the barometer, and horizontal distanced represent inten »I 

time. The curve traced on the card shows the way 
in which tin- height of the barometer has varied dm 

the past week. 

In now, we similarly represenl the way in which the 

point of an alloy varies with its composition, 

honld obtain, in m;my i a CUTVe in 

n in Pig. 1//. Careful invest i- 

gation ha- shown that f: re the cases in which 

chemical combinat: I olid 



TWO METALS BETTER THAN ONE 

which separates out when the fused alloy begins to 
solidify is either pure A or pure B, never a compound 
of the two metals. 

In the cases where the two metals do form a com- 
pound, the curve showing the variation of freezing-point 
with composition is of a different character ; there is 
then an intermediate branch of the freezing-point curve, 
shaped more or less like a camel's hump (see Fig. 16). 
The temperature corresponding to the summit of the 
hump is the freezing-point of the compound which is 
formed, and the composition of the alloy which has 
this maximum freezing-point gives the composition of 
the compound. 

It is interesting now to find that the existence of 
compounds of mercury and sodium, and of gold and 
aluminium, which we suspected from their behaviour on 
mixing, is confirmed by a study of the freezing-point 
curves for alloys of these metals. In the case of mercury 
and sodium the freezing-point curve has a hump the 
top of which is far above the freezing-point of either 
constituent, so that the existence of a compound is 
here proved very definitely. 

The freezing-point curve for alloys of gold and alu- 
minium has actually two separate humps, showing that 
these metals combine to form two compounds with 
different proportions of the constituents. One of the 
humps corresponds to the formation of the beautiful 
purple alloy already referred to, and it is very remark- 
able that this compound, containing 20 per cent, of 
aluminium, should melt at the same temperature as 
pure gold. 

Another method of investigating the nature of alloys 
which has recently been employed with success is the 

80 



TWO METALS BETTER THAN ONE 

study of their structure with the aid of the micro- 
scope. It' a section of an alloy i*> polished, treated 

with a little acid or other corrosive liquid] so as to 
bring out the details on the surface, and put under 
the microeoope, our can obeerve an outline of crystalline 

Structure which cannot be detected by the unaided ( \ v. 

Those wlio have experience in this sort of investigation 

actually distinguish the various kinds of crystals 

which have separated while the alloy was pacing from 
the tu-ed to the M)lid condition. 



81 



CHAPTER VIII 
ACIDS AND ALKALIS 

OF the various classes into which chemical com- 
pounds may be divided, acids form one of the 
largest and most important. They get their name 
from the sour taste which is supposed to characterise 
them, but this characteristic is by no means universal. 
From the chemist's point of view, all acids are similar in 
that they contain the element hydrogen, this hydrogen 
being replaceable by a metal. In many cases we can 
actually follow the replacement of the hydrogen in an 
acid by a metal ; as, for example, when a few pieces of 
magnesium ribbon, iron wire, or granulated zinc are put 
in hydrochloric acid — "spirits of salt," as the druggist 
may call it. The acid and the metal attack each other, 
the latter disappears gradually and turns out the hydrogen, 
which comes bubbling off as a gas. What takes place 
might be expressed as follows: — metal acid-* a salt + 
hydrogen, the salt left in solution being magnesium 
chloride, iron chloride, or zinc chloride, according as mag- 
nesium, iron, or zinc was the metal taken. The corrosive 
acid is, in a sense, destroyed by the metal, and the 
plumber's description of zinc chloride as "killed spirits 
of salt " is therefore quite to the point. 

The behaviour of acids in attacking or corroding metals 
is very general, and even domestic illustrations are avail- 
able. Vinegar is a household article, but it is well to 

82 



ACIDS AND ALKALIS 

remember thai it contains a fair quantity of acetic acid. 

which, although not so powerful as sulphuric or hydro- 
chloric acid, is yet able to exhibit the corrosive action 
which is characteristic of acids in general. A drop of 
vinegar left on the surface of a copper saucepan will 

betray itself before Long by the appearance of verdigris ; 

this is acetate of copper, the salt produced by the action 
of the acetic acid in the vinegar on the copper of the 

saucepan. 

The wit of man has hit upon methods of utilising thi 
OOlTOa i ve action of acids on metals, and if properly guided 
it becomes a process of engraving. Suppose we have a 
plate of copper on which we wish to trace some design. 
One simple way of doing this is to coat the plate com- 
pletely with a thin film of wax or other substance which 
*»t affected by acids, and then with a sharp steel point 
natch the required design through the wax. This 
M that the metal surface is exposed where the steel 

point lias removed the wax, so that if the plate is im- 
mersed in an acid bath, say of "aqua fort is " (nitric 
i ). the metal is eaten away along the lines traced by 
the er. When the wax i- dissolved, the metal 

plate i- then found to bear the design intended, flie 
depth of the lines depending on the length of time 
during which the plate has been left in the' bath. 

Such etching of metalfl is characteristic of acids gener- 

alh\ but there is another kind of etching, namely, on 

~. which can be effected by one acid only — that is to 

say, it is a specific action. This very peculiar propel I \ 

ed by hydrofluoric acid, ;i compound of livdrogen 

nent fluorine, which i- combined with lime in 

mineral fluorspar. If a piece of glasi ifl I ith 

parafl \. arid a design fa traced upon thii with a 



ACIDS AND ALKALIS 






sharp-pointed instrument, then on exposure to the vapour 
of hydrofluoric acid the glass is eaten away at the places 
where the wax has been removed. In this way the design 
traced upon the wax is reproduced on the glass, the sur- 
face, however, being deadened where the acid vapour has 
acted. If it is desired to etch without deadening the 
surface, the glass is immersed in a solution of hydrofluoric 
acid ; this treatment leaves the glass polished and clear 
even where it has been etched. 

The process of etching on glass is invaluable to the 
maker of scientific instruments, for it is frequently desir- 
able to have figures marked on glass apparatus itself 
rather than on any scale attached to the apparatus. An 
" ink " is actually sold containing the ingredients necessary 
to produce hydrofluoric acid, and mere writing with this 
on a piece of glass apparatus is sufficient to leave an im- 
pression. 

The constituent of glass attacked by hydrofluoric acid 
is silica. This is the oxide of the element silicon, and 
forms a very large proportion of the rocks in the earth's 
crust. Sand, for example, is impure silica, and the 
behaviour of hydrofluoric acid towards silica is well illus- 
trated by allowing it to act on powdered sand in a leaden 
vessel. The sand gradually disappears, because the silicon 
in it forms a gaseous compound with the fluorine con- 
tained in the hydrofluoric acid. It is difficult to realise 
that the essential constituent of sand may be converted 
into a vapour, but that is what is effected by the action 
of the hydrofluoric acid. 

Bearing in mind this corrosive action of hydrofluoric 
acid on glass, we see that it would be inadvisable to keep 
a solution of the acid in any glass vessel ; as a matter of 
fact, it is usually sold in gutta-percha bottles. 

84 



ACIDS AND ALKALIS 

The more powerful acids have a destructive and cor- 
rosive action not only on metals, bu1 on many other 
substances also, notably on organic materials. The mosl 
outstanding in this respect is sulphuric acid or oil of 

vitriol, an innocent enough looking liquid, which, however, 

1 1 raordinaril v destructive of animal and \ egel able 

tissue, and requires very careful handling, [fa drop of ii 

on the skin and is not at once washed off, a very 

painful wound is produced. Occasional newspaper report I 

show that there are people who regard vitriol throwing as 
a proper way of settling old scores, but from what has 

: said it will be understood that it is a diabolical pro- 
ceeding, and is very rightly scheduled as a crime. The 

ructive action of sulphuric acid on vegetable tissue is 

i when a drop falls on wood. The latter turns black 
and has a charred appearance, just as if it had been 
burned 

Sulphuric acid is characterised by an extraordinary 

Lnesfl far water. It* cold sulphuric acid is added to 

cold water in L, the warmth of their meeting 

is quite remarkable, and the vessel becomes too hot to 

Further, it' a dish containing a little sulphuric acid 

i- I* • d to the ah-, the bulk of the liquid gradually 

inn* -;<-e- , ami if* left Inn- enough the dish would overflow, 

the reason being that the sulphuric acid absorbs from the 

air afl much moMure afl possible, and BO becomes diluted. 
affinity of -ulphuric acid for water is much utilised 

by chemists in order to rendei ibsolutely free from 

moisture. A currenl of hydrogen which is being evolved 
by f on <»f a metal mi hydrochloric acid comes off 

folly charged with irater vapour, but if it i^ made to 

bubble through Bulphurk acid, the water molecule- 

d by tin arid and the hydrogen is obtained dry. 



ACIDS AND ALKALIS 

thorough is the scrutiny that scarce a single water mole- 
cule escapes. 

One property characteristic of acids generally is their 
power to make carbonates effervesce. Here again domestic 
resources will be sufficient to supply us with an illustra- 
tion, for most houses can furnish vinegar and washing-soda. 
As has been said already, vinegar contains a certain pro- 
portion of acetic acid, and washing-soda is nothing else 
than carbonate of soda. When, therefore, we pour a 
little vinegar on washing-soda we bring together an acid 
and a carbonate, and the result is the usual one, namely, 
effervescence due to the liberation of carbon dioxide. 

This production of gas which occurs when an acid and 
a carbonate are brought together is applied very ingeni- 
ously in the chemical fire-engine. The essential parts of 
this engine are a large closed tank, charged with a solu- 
tion of bicarbonate of soda, and, inside the tank, a leaden 
jar containing sulphuric acid. At the proper moment, 
the acid is tipped into the soda solution, and the carbon 
dioxide which is generated exerts a pressure sufficient to 
force water a considerable distance or height. The advan- 
tage of this fire-engine is obviously that the chemical 
forces may be brought into play instantaneously ; there 
is no necessity to wait until the steam is up. 

The action between an acid and a carbonate may be 
used in another way in the direct extinction of small fires. 
It is well known that combustion is not possible in an 
atmosphere of carbon dioxide, hence if we can surround a 
piece of burning wood, for example, with such an atmos- 
phere, we may smother the fire. This is the object of the 
fire grenades which are to be seen hanging in factories 
and public buildings. They contain the substances 
necessary for the production of carbon dioxide, and these 

86 



ACIDS AND ALKALIS 

are brought together by throwing down and breaking the 
glass vessel in which they arc contained. 

The reader ifi doubtless aware thai much of our 
building material consists of Limestone, the chief con- 
stituent of which 18 carbonate of' lime. Bath .stone and 
dolomite, tor example, are affected by acids in exactly 
the same way as ordinary carbonates, and inasmuch a 
the air in our large towns contains some acid constituents, 
derived mostly from the sulphur in coal, calcareous or 
chalky stones like these are liable to disintegration. 'Hie 
Hou Parliament and York Minster furnish examples 

of the way in which a calcareous building stone decays 
under the influence, amongst other factors, of the acid 
stituents of the atmosphere. 

Bearing in mind another general characteristic of adds, 
we have a very simple clue to a conjuring trick which 
seem- marvellous to the uninitiated. It is found that 
getable products assume one definite colour 
in the presence of acid-, and another colour in the 
nee of alkali-, which, as we -hall see presently, are 
the exact oppo-ite- of acid- in many respects. A solution 
of litmus, f< iple, is turned red by acid-, and blue 

•olution of phenol phthalein is colour- 
in the presence of acid-, and intensely red in the 
presc: alkali-. The-c substances are called in- 

dicator-, and are of the g] in chemical work, 

because they enable the chemist so to neutralise any 

M'on that i -id nor alkaline. In the 

conjuring trick i--«-- an I out alter- 

|y with acid and alkali, and then water containing 
>1 phthalein is poured from the first glass 

i. from the second into the third, and -o 
What tl l ator .see- and marvel* ;«t is a 



ACIDS AND ALKALIS 

colourless liquid becoming suddenly red on being poured 
into an apparently empty glass, and the same red liquid 
becoming colourless again when poured into another 
also apparently empty glass. 

As a class, alkalis are the opposite of acids, not only 
in regard to the indicators just mentioned, but in many 
other respects. The addition of an alkali to an acid 
destroys or neutralises the characteristic properties of 
the latter, and if the right quantity is added the solution 
then contains nothing but a salt — a kind of neutral 
substance which does not exhibit the behaviour either 
of an acid or of an alkali. The process of neutralisation 
may be represented in the following way : acid + alkali ->a 
salt + water; from which it will be seen that the same 
sort of body is produced in this way as is formed by the 
action of an acid on a metal. 

In certain circumstances an alkali may obviously be 
used as an antidote to an acid ; if, for instance, a drop 
of an acid is allowed to fall on clothing, the production 
of a stain, and ultimately a hole, may be prevented by 
the immediate application of an alkali, for the salt which 
is thus formed is quite harmless so far as any action on 
the cloth is concerned, and may be washed out with 
water. Again, if any acid has been swallowed, an 
alkaline substance is the thing to take. In both cases, 
however, the right alkaline substance must be chosen, 
otherwise the cure may be worse than the disease ; for 
certain alkalis have a very powerful action on animal 
and vegetable tissues, destroying such things as skin 
and paper. Two alkalis of this description are caustic 
soda and caustic potash, which, although extensively 
used in the manufacture of hard and soft soap respec- 
tively, are perhaps not so familiar to most people as 

88 




Co. 
I I . i ; I . 
The moat 

from Mr*:] botl 
also caustic soda to ab-orb the 



ACIDS AND ALKALIS 

the 10-called w mild* alkalis, carbonate of soda and 

carbonate of potash. 

What has been said about an alkali acting as an 

antidote to an acid wfl] enable the render to understand 

that air containing carbon dioxide may be purified by 

ring over caustic soda. Tor carbon dioxide is an 

acid gas, and as such IS readily absorbed by an alkali. 

Hence it is possible to devise an arrangement whereby 

rson may breathe in a closed space without Buffering 

from accumulated carbon dioxide. It is only necessary 

that oxygen should be supplied to replace vrhal i> 
absorl>ed in the lun^s, and that the exhaled air should 
be freed from carbon dioxide by contact with alkali 
before it i- again inhaled. Both these condition- are 
fulfilled in the so-called oxygen respirating apparatus. 
This consists of a bay of air carried on the breast and 
Elected by various tubes with (1) the mouth and 
I) a compartment filled with alkali, and (•>) 
cylinder- containing compressed oxygen and carried on the 
back. Any (Hie provided with a portable apparatus of 
this description is independent of the surrounding atmo- 
phere, and may there for e venture into place-, entrance into 
which would ordinarily mean certain death. An equip- 
ment of this kind iras used with success in the 
worl bus the reader may n member, a 

mine disaster occurred not very long ago. 
B t we must return to the question of the well-known 
alkalis. Solution- of these substances are soapy to the 

ii. and H'ly Useful for cleaning pUipO 

r, which diould not be cleaned with 

alkali is the modern aluminium ware used for cooking. 

Of the few metals which are dissolved by alkali-, 

aluminium 



ACIDS AND ALKALIS 






Potash furnishes an interesting illustration of a useful 
substance coming from unlikely sources, of which two 
may be mentioned. Wood contains a certain proportion 
of potash, absorbed from the soil by way of food, and in 
countries which are well timbered potash is extracted 
from wood ashes, in which there may be as much as 10 
per cent, of the alkali. Its very name is derived from the 
fact that the wood ashes are dissolved in water and the 
solution is evaporated down in iron pots. 

Another and still more strange source from which 
potash is derived is the fatty matter in the fleece of sheep. 
This " stunt," as it is called, contains quite an appreciable 
amount of the potassium salt of an organic acid, and 
when this is extracted, evaporated, and strongly heated, 
potash is left behind. 

Besides the mild and caustic alkalis which have just 
been described, there is what is known as the " volatile 
alkali w — ammonia. Although this substance is a gas 
composed of nitrogen and hydrogen, it is an alkali just as 
much as caustic potash or washing-soda. It neutralises 
acids and exerts the same effects as other alkalis on litmus 
or phenol phthalein. 

One of the most remarkable properties of ammonia gas 
is its extreme solubility in water. If a flask quite full of 
the gas is uncorked with the mouth under water, the 
latter will rush in and occupy the whole of the flask just 
as if there had been nothing there at all. Measurements 
have been made of the solubility, and it has been found 
that one cubic inch of water will absorb at the ordinary 
temperature as much as 700 cubic inches of ammonia 
gas. The solution so obtained may therefore be regarded 
as a convenient and compact form of ammonia, and it is 
this which is supplied to us when we ask for ammonia at 

90 



s 



ACIDS AND ALKALIS 

the shops. The liquid we buy contain- a large proportion 
of water, hut it would clearly he impracticable to buy 
and sell ammonia in the pure gaseous state 

Thi- convenient way of handling a substance in solution 

instead of in the pure, undiluted state is employed also in 
the case of some of the adds. Oil of vitriol, to be sure, 

is almost pure sulphuric acid, hut "aqua fort is " fa only 
•lution of nitric acid, and "spirits of salt," a> a rule, 
- not contain more than one-third of its weight of 
hydrogen chloride, which is itself a 

Ammonia, as an alkali, has the power of neutralising 
■Clds, and an interesting experiment which shows that the 
process o\ neutralisation leads to the formation of an 
entirely new substance, a Bait, is the following :- 

cylinder is tilled with ammonia gas, and dosed with B 
glass p| similar cylinder is filled with hydroj 

chloride, and the two are placed mouth to mouth with 

the glass plate between. If the glass plate is dipped 

olourles8 alkaline gas in the one cylinder 

and the colourless acid gas in the other immediately 

ind a white, powdery substance, 
ammoniac, is prod Here pre have the interesting 

uniting to form B -olid, entirely 
different in character from the original reacting sub- 

stain 

Lime is .mother alkaline body, of which enormou> 
quantities are required in the arts and manufactures, and 

majority of people know very little about it 

\aluable prop ' idr of the metal 

calcium, and is obtained by strongly heating carbonafa 

lime, which supplies in profi: nre and in 

narble, linn nd chalk. We 

may note ti point of vie* of ultimate cbemj 

91 



ACIDS AND ALKALIS 



the 



composition chalk is as good as marble ; it is only the 
poor brother in the family. 

By dropping a little acid on marble, limestone, or 
chalk, we can satisfy ourselves that they give an effer- 
vescence of carbon dioxide. As a matter of fact, carbonate 
of lime is just a neutral salt formed by the union of the 
alkaline lime and the acidic carbon dioxide. This salt, 
however, differs from other common salts, because when 
it is heated it gives oft* its acidic component, the 
carbon dioxide, while the lime remains behind. This 
chemical change is carried out on the large scale when 
limestone is strongly heated in lime-kilns ; the process is 
termed "lime-burning." The reader must not suppose 
that lime burns in the sense that a piece of coal does ; 
the term refers only to the strong heating to which 
the limestone is subjected. The product of lime- 
burning is called "quick" lime, but for a great many 
purposes, such as the preparation of building mortar, 
this must be converted into " slaked " lime by the action 
of water. 

The slaking of lime is a beautiful example of the 
changes brought about by a simple chemical action; 
for if a little water is sprinkled on one of the hard 
lumps of quicklime obtained from a lime-kiln, some 
remarkable effects are observed. For a minute or two 
nothing is apparent, but presently steam rises . from the 
lime, and if the observer touches the mass with his 
hand he will realise that much heat is being generated. 
The chemical forces at work are such that the hard 
lump of lime splits up and crumbles down to a soft 
powder, which is absolutely dry in spite of the added 
water. The secret of this striking phenomenon is that 
a new chemical compound has been formed ; the water 

92 




Cold water is poured on a ha: 
team eve 

un are 

ally it 
into a heap of d' 



ACIDS AND ALKALIS 

has united with the quicklime to produce slaked lime: 
hence its disappearance. 

The slaking of lime is accompanied by a consider- 
able increase in bulk, and tin's fact has been occasion- 
ally applied in the blasting of coal in fiery mines, 
where the use of ordinary explosives is dangerous. A 

illcd "cartridge* of quicklime is pressed into a 
cavity drilled in the coal, and water is then forced in 

I pump. The result is that the lime slakes, and 
the bice of the expansion which accompanies the slaking 

■ess is >ueh as to split the surrounding niaves of 

— an excellent example this of the chemical enei 
latent even in the most commonplace materials. We 
do not usually associate anything very striking with 
such matter-of-fact substances as lime and water, and 

iii their own quiet way they can together do the 
work tor which the aid of a high explosive is generally 

lisitioned. 
Lime i- wry extensively employed in the prepara- 
tion of building mortar. For this purpose sand and 
flaked lime are used, and they are made up together 
with water until the mixture has a pasty consistency, 
ting of mortar which occurs a few days after it 
hai been made and applied fa simply a procesfl of drj 

OSUre to the atmosphere. But e\'en after the 

mortar hat lei it undi further change — it gradu- 

ally hai This p. >f hardening is a chemical 

and i- due to the dow ab-orption of carboo dioxide 

from the atmosphere. 

J- m • isOy be ihown thai lime has the power of 
absorbing carbon dioxide, for if lime water, which i 
ply a clear solution of daked lime, is ex p os e d to 

the air : time, a white film of chalk collect- on 



ACIDS AND ALKALIS 

the surface. So also the lime in mortar gradually 
absorbs carbon dioxide, becoming converted into the 
hard carbonate of lime. It will, of course, take a very 
long time for the hardening to be complete, but the 
examination of ancient mortar from Greek and Roman 
ruins has shown that in these cases the carbon dioxide 
absorbed from the atmosphere has been sufficient to 
convert all slaked lime into the carbonate. In fact, 
by pouring a little acid on a piece of old mortar any 
one can see that it contains a carbonate. Every stone 
or brick wall, therefore, in which mortar has been used 
must be pictured as the scene of a slow, imperceptible 
chemical change — a change which will probably go on 
as long as the wall lasts. 



94 



CHAPTER IX 

NAIL HAL WATERS, AND WHAT THEY 
MAY CONTAIN 

IT was a commonly-accepted idea anions the ancients 
that fire, air, earth, and water were the tour elements. 

the Simplest forms which matter could assume. This 

lusion was not leached as the result of experi- 
ments of unsuccessful attempts to get at something 
more simple ; for the ancient philosophers never made 
any chemical experiments at all. So far as they con- 
cerned themselves with the science, they were what we 

lit call "study-table chemists/" and they thought 

it a much finer thing to make theories than to make 

experiments. To indulge in the latter practice was re- 

an occupation quite below the level of a 

philosopher. Now all thlf ha- changed, and in the 

tWO Centuries men have Used the experimental method 
with infinite skill and patience to wring from Nature 
many of her most valuable secrets. Amongst other 

things, it fa .1 discovered that water is not an 

element, as the ancients thought, but i^ capable of 
being brok» D into \et simpler and muiv elemen- 

tary ml . hydrogen and oxygen. So far, then, 

the ancient ong, but at the same time they 

were correct in n 0O€ of the first- 

rank • meet in Nature, not only because it 1 

90 



NATURAL WATERS 

abundant, but because it is so absolutely essential to 
life of all kinds. 

From the chemists point of view, water is an ex- 
ceptionally interesting substance. For, in the first place, 
it furnishes an excellent example of the thorough-going 
alteration which matter may undergo when it takes 
part in chemical processes. Think of it. Hydrogen 
and oxygen, the elements which combine chemically to 
form water, are gaseous, invisible substances which we 
may mix without any obvious change taking place. In 
the mixture neither gas interferes with the other, and 
each retains its own characteristics and properties. But 
bring a lighted taper or match near the mouth of the 
vessel which contains the gases, and what is the result ? 
The gases, which have up to this point been in peace- 
ful contact, are stimulated to mortal combat, a loud 
explosion occurs, and the gases are destroyed, leaving 
behind only the sweat of battle in the shape of a few 
drops of water. One has seen a conjurer converting 
handkerchiefs into rabbits, and a pack of cards into 
thin air, but his feats are tricks after all, and the more 
genuine cause of wonder is to be found in the marvel- 
lous things which Nature has to show. Among these 
marvels are such changes as that by which hydrogen 
and oxygen are converted into water, a substance with 
absolutely new properties and characteristics. 

Water, however, is interesting in other ways. Has 
the reader ever observed that ice floats in water ? He 
may have seen it, but not perceived it. Probably the 
fact has just been accepted as a matter of course, without 
any inkling of its importance. But the truth is that 
water is somewhat eccentric in this respect. Generally 
speaking, when any substance is exposed to lower and 

96 




^» ,tf g 



! 



NATURAL WATERS 

lower temperatures, and thereby passes from the con- 
dition of a gas to that of a liquid, and from the con- 
dition of a liquid to thai of a solid, it shrinks and becomes 
more dense — that is, a given bulk of the substance weighs 

more and more. Water, however, is peculiar. As the 
temperature fall-, it changes from steam to liquid water, 
and from liquid water to iee. hut there is not through- 
out these changes a continuous increase of density. 
Water does indeed become more and more dense down 
to a certain point, 89° Fahrenheit, but here it rev< 
its behaviour; it expands and becomes lighter as it 
colder. So it comes about that ice is lighter than 
the water from which it freezes, and accordingly floats 
on the surface of the water. A little thought will show 
bo* significant this fact is in the economy of Nature, 
fur the preservation of life in our lakes and seas during 
winter is possible only because the surface ice 
protect iter underneath from freezing. 

Ti, t, however beneficial in its consequent 

in the realm of Nature, is liable to put us moderns 
sometimes to considerable inconvenience. We fit our 
houses with water-pipes, and it is only when the grip 

inter ha- been unusually severe and our pipes are 

burst, that we learn that Nature will have her way in 
spite of our devices. Since ice occupies more i 
than the same weighl of water, the pipes air burst 

when the water freeze-, although it 1S not till the thaw 

that the damage is revealed to us, 
Now the waters with which Nature supplies us, not 

llarlv. according to our way of think; 

• : pure from the chemist's point of dew. Many 
of them h and quite suitable for drinking pur])-' 

but even th in sub I I ri< h m il e I hem a little 

G 



NATURAL WATERS 



« 



different from pure water. Thus it is well known that 
practically all natural waters contain in solution an 
appreciable amount of solid matter. A large part of this 
solid matter may be deposited when the water is boiled, 

£ and a glance inside the kitchen 
kettle will, in many cases at 
least, suffice to show that this 
is the case. The so-called 
" furring " of a kettle is 
simply due to the solid 
matter depositing when the 
water boils. The same thing 
happens in engine boilers, and 
the incrustation or scale that 
forms on the plates of the 
boiler is a cause of serious 
trouble. For it is very diffi- 
cult to remove the scale with- 
out damaging the boiler, and 




so long as it is allowed to 



Fig. 2. — Showing the relative 
amounts of solid matter dis- 
solved in various waters. 



remain extra heat must be 
supplied to the boiler if the 
output of steam is to be main- 
tained. The extra heat is 
required because the scale is a bad conductor of heat ; it 
has been found that a boiler incrustation one quarter of 
an inch in thickness involves a consumption of fuel 
50 per cent, greater than would be required if the boiler 
plates were clean. 

Different natural waters contain quite different amounts 
of dissolved solid matter. Some, such as sea water, con- 
tain a great deal ; others, such as rain water, contain 
very little. A good idea of the relative average amounts 

98 



NATURAL WATERS 

of solid matter contained in fresh waters from various 
sources will be obtained by a glance at the accompanying 
diagram. Hie heights of the columns are proportional 
to the amount^ of solid matter in the various waters. 

Deep-well waters contain on the average about half an 
ounce of solid matter for every thousand ounces of water, 
and the proportion of solid matter in the other fresh 
waters may be roughly gauged from the diagram. It" the 

amount of solid in sea water were to be represented in the 
ty, a column eighty times as high as the highest in 
the diagram would have to be introduced. This obviously 
must be left to the imagination of the reader. 

ordinary individual, waters are familiar as 
"hard" or "soft/* and this classification gives a rough 
idea of the amount of solid dissolved in the water. Haiti 

waters contain a large amount of solid ; soft waters, which 

require but little soap to make a lather, are those which 

air comparatively free from dissolved solid. 

The question next arises, what are the solids that we 

find in the various natural waters, and where do they 

come from ? It' sea water is left out of account for the 

L-nt, it may be said that the main substances occurring 

in natural waters are sulphate and carbonate of lime (ami 

ia, to a Ie8fi extent). The plopoit ion of tlw-e 

tances held in solution by a water depends on its 
»rv. 
fcdfl a matter of fact, carbonate of lime (chalk) is not 

soluble in pure water, but only in water charged with 

lioxide If now the reader recollects that t). 
i opportunity for rain to become charged with carbon 
dde from th< phere, he will understand that the 

water which falb on th» of the earth and percolate 

through the oil and the rock- will haw the |<< 



NATURAL WATERS 

dissolving from these the carbonate of lime which they 
contain, as well as more soluble substances. When this 
water comes to the surface again in a well or spring it is 
found to be hard. But the simple process of boiling may 
render it comparatively soft, since in this operation the 
carbon dioxide with which the water is charged is boiled 
out, and the carbonate of lime, being no longer soluble, 
is deposited. That the " furring " in the aforementioned 
kitchen kettle is caused by a carbonate is shown by the 
effervescence which occurs on the addition of a little 
hydrochloric acid — " spirits of salt," as it is commonly 
called. 

Apart from actual boiling, mere exposure of such a 
hard water to the air will deprive it of its carbon dioxide 
by evaporation, and in so far as the carbon dioxide is 
removed, in so far is a deposit of carbonate of lime pro- 
duced. This is the way in which these curious excrescences 
known as stalactites and stalagmites are formed. Water 
which has percolated through some depth of soil and 
rock, and become hard in the process, may arrive at the 
roof of some underground cavern. The drops which 
there form are subject to evaporation, and part of the 
carbon dioxide with which they are charged is removed. 
This leads to the deposition of chalk, and a tiny contribu- 
tion is made to the growth of the stalactite. A further 
quantity of carbon dioxide evaporates as the drops fall on 
the floor of the cavern, a further deposit of chalk is 
formed, and a tiny contribution is made to the growth of 
the stalagmite column. 

Another very interesting natural phenomenon closely 
related to the formation of stalactites and stalagmites is 
the action of what are known as " petrifying springs. 1 ' 
If a wicker basket, for example, is exposed to the action 

100 




\V } 1 1 
The entrance to the recently explored tta I 



NATURAL WATERS 

., it is gradually impregnated and coated 
with a stony-like substance. The explanation is that tin* 

4 a petrifying spring i*> bard, and contains a con- 

siderable quantity of carbonate of lime in solution. When 

the ' miic- to the surface it depoeitfi carbonate of 

cause it loses by evaporation some of the carbon 

dioxide in virtue of which it has the power of dissolving 

bstance. This deposition of calcareous matter 
may take place on any objects, such as leaves or twi 

to the play of the water, but it IS thought by 

eople that certain bog-mosses or water-plants are 

specially < Rective in causing decomposition of the carbonic 

.and thereby inducing the deposition of a crust of 

carbonate of lime on their stems and branches. 

Mosl of the water which has percolated through the 
-oil and the rock-, and thereby collected a certain amount 

olid matter, find- it- way into stream- and rivers 

ultimately into lake- and seas. It will be obvious 

mount of -olid matter in the -ea and in 

- which have no outlet mu-t be gradually increasing, 

the supply of water is roughly balanced by continual 

: -oration from the surface. The rate of increase of 
the -olid- in sea water i- very small because of the 

[Uantlty of water, but in the ea-e of an 
inland lake in a hot climate, where there are h< 

rains alternating with periods of rapid evaporation, the 

. ml of dissolved solid is very high and incn 
ly rapidly. 

Tip I ) id Sea i n in point. It- watei i are 

brackish, and contain no less than about 

■ (ji • their wight of solid matter, mostly -odium 

chlo nmon -alt) washed OUt bom the neighbour- 

hill-. The proence. of o much olid makes the 

101 



NATURAL WATERS 

water of the Dead Sea considerably heavier, bulk for 
bulk, than fresh water ; it is so dense that eggs will 
float in it, and it will not allow the human body to 
sink, Ordinary sea water also is somewhat denser than 
fresh water, and its superior buoyancy is possibly known 
already to the reader by personal experience. 

Much of the water which is distributed over the 
surface of the globe is quite unsuitable for the use of 
man. All brackish waters come under this category ; 
and many an unfortunate sailor who has been cast adrift 
at sea has realised the bitter truth that there was " water 
everywhere, but not a drop to drink. " Even from sea 
water, however, it is possible to obtain pure water by 
the process of distillation. The water is boiled in a 
suitable vessel, and the steam is led away through a 
cooled pipe, at the end of which the condensed water 
may be collected in a pure state. The solids dissolved 
in the sea water are not volatile, and are accordingly 
left behind in the boiler. At the present day much of 
the fresh water required on board our great ocean liners 
is obtained by subjecting sea water to distillation. 

When one thinks of it, Nature herself is constantly 
making use of this process. The evaporation that 
continually takes place from the surface of the ocean 
is really a slow distillation ; the water vapour condenses 
into clouds, and falls, some of it at least, as rain on 
the surface of the land. Rain is natural distilled water. 

For many domestic and industrial purposes it is 
necessary to purify even ordinary fresh water, especially 
when it is hard. This process of " softening " water 
may be effected in several ways. It has already been 
stated that mere boiling will diminish the hardness of 
a water, but even water that has been boiled will not 

102 



NATURAL WATERS 

at once give a lather with soap. Instead of giving an 
immediate lather, a curd ia formed — evidence that the 
sulphate of lime still remaining in the water is being 
removed or precipitated by the soap. Only after this 
removal is complete will the K>ap form a lather. 

The lime in a hard water may be removed also by 

the addition of sodium carbonate — washing-soda, 

it is commonly called — or of lime water. If the water 
he obtained free from the deposit of chalk which 

hoth these substances produce, it must be allowed to 

stand in tanks, and then run off after the precipitate 

has lettled bo the bottom. 

tonally the impurities in a water are of an 
■nic nature, and these may be such as to render the 

water unsafe for drinking purposes. This organic matter 
may oom4 from decomposing vegetable substances, or it 

of animal origin, and come from sewage or surface 
drainage. Sometimes our senses of taste and smell will 
warn as of this, but in the last resort we must depend 

on a chemical and bacteriological examination of the 
water. Such an examination will reveal, in the case of 

r, an unduly high amount of nitrogenous 
compounds, and possibly also large numbers of disease 

make the water safe, it mibt either be filtered 
through land or unglazed porcelain, or it must be sterilised 

by boiling. All germs seem to find exposure to boiling 
wab snewhat trying experience, and few survive 

the ofdeaL Tin- will be clear from b special example 

which b put on n cord. 

A particular water of bad quality was found to contain 
germs per cubic centimetre. Exposure to a 

tem: 194 Fahrenheit for ten minute- reduced 

the number tin n hardy individuals 

in.; 



NATURAL WATERS 

had to give up when the water was boiled for ten 
minutes. As the palatable quality of a water depends 
on the quantity of dissolved gases, such as oxygen and 
carbon dioxide, the device of boiling it renders it some- 
what insipid. If this is considered a disadvantage, it 
can be made more palatable by aeration, that is, by 
shaking it for a little with air. 

Besides the various kinds of fresh water and the 
brackish water of our seas and inland lakes, Nature 
supplies us here and there with waters of a peculiar 
kind, distinguished not so much by the quantity of 
matter which they contain as by the fact that this 
matter is of an unusual kind. There are the so-called 
"mineral waters," which, in many cases at least, come 
from considerable depths below the surface, and are 
frequently hot on that account. Some of the well-known 
mineral waters are alkaline and contain carbonate of 
soda, notably those which are charged with extra large 
quantities of carbon dioxide, such as Apollinaris and 
Seltzer waters. Carbon dioxide has been forced into 
these waters under high pressure far below ground, and 
when they come to the surface and under the lower 
pressure which prevails there they cannot contain them- 
selves, as it were, and so are marked by their characteristic 
effervescence. 

Here and there one finds iron or chalybeate springs. 
Carbonate of iron, like carbonate of lime, is not soluble 
in pure water, but is taken up by water charged with 
carbon dioxide. Thus it is possible to obtain a water 
which holds in solution a considerable quantity of other- 
wise insoluble iron. When such a water comes to the 
surface, it loses some of the carbon dioxide with which it 
is charged, and the channel down which the water runs 

104 






NATURAL WATERS 

tinged a yellowish or reddish colour, owing to 
the action of tl en in the air o\\ the carbonate of 

iron deposited from the spring water. 

Saline springs containing sulphate of magnesia and 

sulphate of soda are frequently found. The waters of 

these springs are bitter and ad as purgatives. It is 

interesting to note thai sulphate of magnesia is commonly 

Epsom salts, on account of the fad thai it was 

found in a spring at Epsom by a London physician of the 

iteenth century. There are springs of this class in 

other parts of England, bui the best known spas at which 

bitti \ are available are Sedlitz, Friedrichshall, and 

ringen. 

Other mineral waters which are peculiar are those which 

contain sulphur in some form or other; the spring al 

Harrogate and Strathpefier are the best known of l he 

kind in this country. Owing to the sulphuretted 

hydrogen and the sulphide of soda which these wai 

contain, they have an unpleasant taste and smell, but 

are much \ alued for their medicinal properties. 

Those happy individuals, however, who have hitherto 

the ills to which flesh is heir, will have no desire 

to cultivate a closer acquaintance with sulphur springs. 



105 



CHAPTER X 

CHEMICAL CHANGES WHICH PRODUCE LIGHT 
AND HEAT 

TO the popular mind a chemical laboratory is 
suggestive of explosions — reactions which result 
in the very evident production of light and heat, 
and sound into the bargain. But it is not necessary to 
visit a chemical laboratory in order to observe chemical 
changes which produce light and heat, for we are all 
chemists to some extent, at our own firesides. When 
we strike a match or light a fire we make a chemical 
experiment, but the " Red Flower " is so familiar to us 
that we miss the meaning and the marvel of it. 

The making of fire is one of the oldest chemical 
achievements of the human race, and in our modern world 
the part played by combustion is of enormous importance. 
A little thought will show it is on those chemical changes 
which produce light and heat that we depend for a great 
many of our modern social conveniences. Where does 
the power come from which drives our motor cars ? 
Why, from the combustion of petrol. Further, when a 
man stands on the footplate of a " Flying Scotchman," or 
in the engine-room of the Mauretania, he begins to 
understand what wonders in the way of locomotion we 
owe to the combustion of coal. 

" Ah, yes ! " some reader may say ; " but we are going 
in for electricity nowadays, are we not ? We are lighting 

106 



PRODUCTION OF LIGHT AND HEAT 

our street- with electric light instead of gas, and our 
railways are being electrified." Thai is all quite true, 
but e\en then we have not got rid of combustion as the 
source of nearly all our energy. Except where water- 
power is available, the introduction of electricity means 
-imply that the combustion ha- been centralised. In- 
stead of burning gas at eaeh street lamp, we burn eoal 

j I- at some central furnace, and use up the energy of 

bustion in driving a dynamo; instead of having a 
tire on eaeh locomotive we have again a central furnace 
at the power-station. Hence the production of energy, 
whatever its form, —till depends almost exclusively on the 
time-honoured process of combustion. 

Now, although the various things which are burned for 
the purpose of producing light and heat are outwardly 
very different— gas, coal, paraffin oil, candles, wood, 
methylated spirits, petroleum, peat, &C — the process of 

bustion is essentially the same in each case. The 
substances just mentioned are alike in containing carbon 
and hydrogen, either in the form of the elements them- 
selves, or in the form of compounds, and the process of 
combustion i- -imply the chemical combination of these 

elements with the oxygen of the atmosphere. Hence, 

if we Understand what happens in the combustion of a 

candle, for example. WC should be able to give an intelli- 

explanatioo of what takes place in a paraffin oil 

lamp or in a coal file. 

When the carbon and hydrogen in a candle combine 
with tb of the atmosphere, the product- are our 

old * carbon dioxide and wat rbon dioxide i- 

an invisi ader will remember, and the 

Krmed in the flame is given off a- an invisible 
vapour. The candle, paduallj disappi 

107 



PRODUCTION OF LIGHT AND HEAT 

it burns, leaving little or no trace behind. To the super- 
ficial observer the fact that the candle disappears and 
leaves nothing tangible in exchange might seem to throw 
doubt on the law of conservation of matter, according 
to which matter cannot be destroyed. But it will be 
admitted that the law would still be fulfilled if the dis- 
appearance of so much matter in one form were com- 
pensated by the production of an equivalent amount in 
another form ; and the reader who has followed the argu- 
ment of the foregoing chapters will recognise that some 
forms of matter are invisible. 

The fact is, the invisible products of the combustion of 
a candle— that is, the carbon dioxide and the water vapour 
— weigh more than the candle. This is only natural, for 
just as it takes two to make a quarrel, so there are two 
parties to a combustion, namely, the combustible substance, 
in this case the candle, and the supporter of combustion, 
the oxygen from the air. As the combustion consists in 
a combination of the carbon and hydrogen of the candle 
with the oxygen of the air, the products are necessarily 
heavier than either the candle or the oxygen separately. 
The chemist can easily show that this is so by absorbing 
and weighing the carbon dioxide and water, but it will 
be sufficient for our purpose to show that each of these 
substances is present in the gases arising from a candle 
flame. 

In order to show that carbon dioxide is one product of 
a candle flame, we may fix a small piece of candle on a 
wire, light the candle, and lower it into a glass jar, into 
which w r e have previously poured a little lime water. 
When the candle has been allowed to burn in the jar for 
ten or fifteen seconds, it is taken out, the jar is closed by 
a cork, and the contents are shaken. It will then be 

108 



PRODUCTION OF LIGHT AND HEAT 

Been thai the lime water has become turbid, showing that 
the air left in the jar after the burnifig of the candle 

contained carbon dioxide. 

The production of water in the flame of a burning 
candle may be very readily demonstrated with domestic 
apparatus. A tumbler of cold water, the colder the 
better, is carefully wiped on the outside no that it is 
perfectly dry, and is then held a little above the candle 
The outside of the tumbler at once become-. 
cloudy owing to the condensation of tiny drops of water. 

The extent \o which carbonaceous fuel i^> converted into 
carbon dioxide and water depends on the supply of the 
air which supports the combustion. It' for any reason 
Ripply of air is cut off, combustion ceases. Hence it 
COmes that a candle cannot- continue to burn in a closed 
than a very short time. Not only does it 
oist the oxygen, but by its own combustion it pro- 
duces substances which are unfavourable to a continuance 

of thep In an atmosphere of carbon dioxide and 

water vapour no combustion is possible. On the other 
aore air or oxygen we supply to the burning 
fuel, the more complete' is the combustion. 

The oldest method of supplying more air to burning 

furl, and thereby securing more complete combustion, i^ 

familiar one of making a draught The difference 

an oil-lamp flame with the chimnej off, and the 

e flame with the chimney on. fa due to the draughl 

which tla- chimmy makes : this draught means an inrudi 

' tom of the chimney and a bet ter supply 
o th.- flame of the burning oil 
ps the reader ha- 1 1 ied M>metim< to fan the 
flickering flame of a newly-lit !ii< l<\ boldi .p. r 

of th. I . [| of 

10!) 



PRODUCTION OF LIGHT AND HEAT 

this is that the chimney draught sucks the air right 
through the fuel, which is thereby fed more perfectly 
with the oxygen it so badly needs. If the newspaper were 
not there, the bulk of the air which is drawn up the 
chimney would come in through the upper part of the 
grate front, without passing through the fuel. The 
village blacksmith, too, when he makes his bellows roar, 
is in quest of more rapid combustion, and consequently 
more intense heat. 

Imperfect combustion is responsible for the smoke that 
hangs like a pall over so many of our large cities. We 
in England insist on having the cheery but unscientific 
open fireplace, with the result that the fuel is imperfectly 
burned, and our chimneys pour a constant stream of 
smoke into the atmosphere. Smoke is charged not only 
with finely-divided carbon and soot, but also with oily 
and tarry vapour, whereas if there were perfect combustion 
nothing but invisible gases would leave the chimney. 
Just imagine what that would mean ! Apart from the 
saving in fuel, we should never require the services of the 
chimney sweep, and we should be spared many of the 
grimy fogs which come, especially in London, to clog our 
breathing organs and to depress our spirits. 

Why should it be so uneconomical and unscientific 
to burn coal in such open fireplaces as are common in 
England ? The key to the answer lies in the fact that 
when coal is heated it first gives off a quantity of in- 
flammable gas, and it is really this gas which burns when 
we put coal on a fire. But unfortunately in our open 
fires the fresh coal is put on the top, so that the gas which 
comes out of the coal as it gets warmed up is in a part 
of the fire where the supply of oxygen is limited. Not 
only has a considerable portion of the oxygen been used 

110 




A I 



:n the south hen 

they are tapped the petro'eum gttsbei up •■•••' 

these oil fountains catches fire and the r« ibe i ! 1 1 1 - 1 r . t : f tire 

■j feet high 



PRODUCTION OF LIGHT AND HEAT 

ii}) in the combustion of the glowing furl at the bottom 
of the grate, but the carbon dioxide which is produced 

there, and which ascends through the freshly-added fuel, 
makes it impossible to gel perfect combustion of the 
latter. Hence it comes thai quite a respectable fraction 
of our best household coal simply goes up the chimney 
unburnt, to become subsequent^ a nuisance to ourselves 
and our neighbours. 

The abolition of smoke is a consummation devoutly to 
Ik* hoped for, and considerable advance has already been 
made in thai direction. Improvement has been effected 
chiefly in the diminution of smoke emitted from factory 
chimneys. For this we are indebted, partly at least, to 
the introduction of mechanical stokers, which \\i>i\ coal 
into factory furnaces so that the fresh fuel is put where 
it has an excellent supply of oxygen. The mechanical 
stoker subsequently moves the coal on to other and 
hotter part- of the furnace, and it has the further ad\:in- 

that it obviates the necessity of opening the furnace 

■v an operation which involves the admission of I 

draught of cold air. 

Appliances have been devised for securing more perfed 

Comb u stion in house tiles by introducing the coal from 

hut none of these have come into genera] use, 
adoption of such a plan would involve the recon 
-truction of all our fireplaces. 

Another method of getting rid of the smoke nuisance 
i- to subjeel the coal to destructive heating in 
work-, and obtained for h pur 

J. This i- the plan that will probably 

be adopted in the long nut \ gas stove is, however, much 

entimenl cling round 
the old titution will die hafcL 

111 



PRODUCTION OF LIGHT AND HEAT 



^pxaajrS* 



When gas (or a candle) burns in the air, the supply of 
oxygen is not sufficient for complete combustion of the 
carbon and the hydrogen, except in the outermost envelope 
of the flame, and the fact that we get any light at all 
from an ordinary gas or candle flame is due to a host of 
unburnt particles of carbon in the interior. These particles 

are raised to a white heat by the 
flame, and so make it luminous. 
That the ordinary gas or candle 
flame contains particles of carbon 
may be very easily shown by 
holding a cold surface just into 
the top of the flame, when a 
deposit of soot (that is, carbon in 
a finely divided form) is obtained. 
When the supply of air to a 
gas flame is increased by mixing 
the gas with air just before it 
reaches the actual place where 
it is burned, then the combus- 
tion is more complete, the flame 
is hotter and no longer luminous. The particles of 
carbon which ordinarily make the flame luminous are 
now all converted into carbon dioxide, even in the interior 
of the flame, by the extra oxygen supplied. This is the 
principle of the well-known Bunsen burner, which finds 
application now, not only in the laboratory but in our 
houses, on incandescent burners and gas stoves. 

A simple Bunsen burner is shown in the accompanying 
diagram. The current of gas which rushes out at the 
central nozzle sucks in air through the surrounding holes 
at the bottom of the burner, while the mixture of air 
and gas ascends, and is burned at the top of the tube. 

112 




FIG. 3.— A Bunsen Burner. 



PRODUCTION OF LIGHT AND HEAT 

The flame is very hot, gives out almost do light, and if 

a cold surface is put into the Maine, DO BOOt is deposited. 

This kind of Maine IS therefore especially suitable tor heat- 
ing and cooking purposes, for blackening of the utensils is 
avoided. The part played by the air in such a burner 
can be wry simply demonstrated. If the burner is 
lighted and the observer puts his fingers over the air 

inlet holes at the bottom of the tube. 1 lie- flame, instead 
giving practically no light, becomes luminous at 
once. 

If the reader will take the trouble, this little experi- 
ment may be carried out with an ordinary incandescent 
burner. The air inlet holes arc easily discovered, and if 
the burner is lit on M>me occasion when the mantle has 
removed, the effect of letting in or shutting off the 
extra supply of air i^ very evident. 

It has been already stated that an ordinary gas or 
candle Mann- is luminous because it contains particles of 
unburnt carbon which are raised to incandescence, and so 
emit light. If this i> SO, then we may expect that if we 
a non-luminous flame like that of a Bunsen burner, 
introduce into it some -olid substance irhich can 
stand a very high temperature without melting, this flame 
will become a source of light. His is exactly tin- 
principle irhich has been applied in our modern incan- 
descent burners. As hasjusl been pointed out, the flame 
• lit burner, apart from the mantle, is quite 
without luminosity, and the mantle is simply an invisible 
bich is raised to incandescence by the heat of 

the ilai 

A similar device used to be much in vogue for the 
ibition of lantern slides — in tl. died lime-light. 

By allowing a very hot flame to play on a little lump of 

118 B 



PRODUCTION OF LIGHT AND HEAT 

lime, the latter is raised to a white heat, and emits a 
very powerful light. 

In an electric glow lamp the light proceeds from a 
carbon filament raised to incandescence, but in this case 
the source of heat is an electric current, not a flame of 
burning gas. The electric glow lamp furnishes at the 
same time an interesting illustration of what has been 
said about there being two parties to a combustion. 
The filament in the lamp is made of carbon ; there it is, 
glowing brightly, and yet apparently it suffers no wastage ; 
it appears to burn, but it is not consumed. Why is 
this ? Because the other party to a combustion, the 
oxygen, is absent on this occasion. The lamp has been 
rendered vacuous during the process of manufacture — that 
is, the air which it contained was removed — and so no 
combustion is possible. The tender little filament is 
protected by its glass cage from the hordes of oxygen 
molecules that would be only too ready to fall upon it if 
they had the chance. 

It must not be supposed that the term combustion is 
to be applied exclusively to those cases where a carbon- 
aceous fuel is burned. Many other substances combine 
readily with the oxygen of the air, and the chemical 
change involved in this combination produces light and 
heat. 

Everybody who has seen an underground cavern illumin- 
ated by the burning of magnesium ribbon knows what an 
intense light is emitted in this process ; and the process 
is essentially the same as the burning of a piece of char- 
coal. When charcoal is burned, oxide of carbon (carbon 
dioxide) is produced ; when magnesium is burned, oxide 
of magnesium (magnesia) is produced. 

The burning of magnesium illustrates very excellently 

114 



PRODUCTION OF LIGHT AND HEAT 

one or two points which ha\e been mentioned already. 
In the first place, it shows what fundamental changes those 

Klbstances Undergo which take part in ■ chemical action ; 

we start with a piece of metallic ribbon and the invisible 

air, and there is left behind a soft, white, powdery mass 
of magnesia. In the tOCOnd place, the intense light 
obs erved when magnesium burns is due to the presence 
of little particles of infusible magnesia, which are 
rendered incandescent by the great heat of the chemical 
action. 

Again, it is easy to show that just as the carbon dioxide 
and water produced by the combustion of a candle are 
heavier than the candle, so the white powder produced 
by burning a piece of magnesium ribbon weighs more 
than the ribbon. The discovery that the products of 

combustion are heavier than the combustible substance 
really a very important one in the history of chemistry ; 

tor up to about 180 years ago it was generally supposed 
that a combustible substance contained something called 
phlogiston, which came out of the substance when it was 

burned It was the famous French chemist Lavoisier who 

finally Overthrew this theory, and emphasised the fact 
that instead of losing anything when it was burned, a 

combustible substance actually became heavier. 

The meaning of the term "combustion** hac been e\- 

led in the foregone iaphs so (hat the burning 

I the burning of magnesium are brought under 

the jory. We ma\ now extend the Kim still 

further to cowr many chemical pro fhich, although 

they do not \ery obviously produce light and beat, \»t 

. nd essentially on the -ame chemical phenomenon, 

namely, the combination of some Hlbstance with the 

. gen of the atmo phere, 1 

1 1 5 



PRODUCTION OF LIGHT AND HEAT 

bustion, and may be referred to generally as oxidation 
processes. 

One of these processes, which, without producing any 
light, produces a good deal of heat, is the respiration of 
animals. What goes on in our bodies, through the agency 
of the lungs and the blood, is neither more nor less than 
a combustion, in the course of which the carbon com- 
pounds in the body, the fat, &c., are burned to carbon 
dioxide and water. 

It is very easy to show that air expired from the lungs 
is heavily charged with carbon dioxide. Ordinary fresh 
air contains so little of this gas that a pint bottle full 
produces no milkiness when shaken up with a little lime 
water. But if the air which we breathe or blow out from 
our lungs is made to bubble through a little lime water, 
a very marked turbidity appears. Exact measurements 
have shown that whereas fresh air contains 3 to 4 parts 
by volume of carbon dioxide in 10,000, the air which 
issues from the lungs is charged to the extent of 400 to 
450 parts carbon dioxide in 10,000. A little carbon 
dioxide is also given off through the skin, and it is com- 
puted that the total carbon dioxide evolved by the lungs 
and skin is about three-quarters of a cubic foot per hour. 
An ordinary gas burner produces about one and a half 
cubic feet of carbon dioxide in the same time, so that as 
far as the contamination of the air in a room is concerned, 
a gas burner is equal to two men. 

Another change which comes under the same category 
as respiration, and which we might describe as a slow 
combustion, is the rusting of iron. Rusting is the com- 
bination of the metal with the oxygen of the air, and is 
thus exactly parallel to the burning of magnesium ribbon, 
except that it takes so much longer. The total heat evolved 

116 



PRODUCTION OF LIGHT AND HEAT 

in the process of rusting is not any less than it would be 
it' the oxidation took place rapidly ; it is only spread 
OV«r siieli a long time that the evolution of heat at any 

particular moment is not noticeable 

Rusting is an example of spontaneous oxidation. It is 
not necessary i^ strike a match to start the process; rust- 
ing is only too ready, as we often know to our co^t, to 
start on it-- own account. It is, indeed, essential that 
carbon dioxide and moisture should be present before 
rusting can take place, but these substances are both 

-nt to some extent in ordinary air, and the only way 
to keep iron from rusting i^ either to paint it, or to plate 
it with some other metal which is less ready to hold 
traffic with the air. Metals which are commonly used for 
this purpose are zinc, tin, and nickel. Galvanised iron 
and tinplate, which are manufactured in such large 
ire simply iron which has been coated with 

and tin respectively in order to protect it from corro- 
sion. Every cyclist knows that bo long as the nickel- 
plating of his handle-bar^ is intact there is very little 
tendency to tarnish, but that wherever the protective 

r of nickel has been removed rust i- not long in 
putting in an appearance. 



117 






CHAPTER XI 
HOW FIRE IS MADE 

IN the forgoing chapter it has been said that the 
making of fire is one of the oldest achievements of 
the human race. So old is it that there is no trust- 
worthy evidence of any tribe which was ignorant of fire and 
its uses. There is nothing impossible in the supposition 
that there may have been such a tribe, but we have no 
proof. It should be remembered that man must have 
been familiar with fire on the large scale, even before he 
knew how to produce it himself; for we may presume 
that lightning and volcanic eruptions have always been 
features of life on the earth. Apart, however, from these 
exceptional manifestations, the primeval man must one 
day have discovered how to produce fire with the ordinary 
means at his disposal. The reader can imagine the amaze- 
ment and delight, perhaps the alarm, of the first human 
being who succeeded in making fire for himself, and of 
those who afterwards made an independent discovery of 
the same thing. How it was actually done we can only 
conjecture, but we shall probably get fairly near the true 
answer if we can discover the methods of making fire 
which have been practised among primitive tribes even in 
comparatively recent times. 

The ancients solved the problem of the original discovery 
of fire in a manner that has the merit of simplicity, even 
if it does not commend itself to the scientific mind of this 

118 



HOW II HE IS MADE 

twentieth century, They supposed thai fire had been 

stolen from heaven by Prometheus, who carried it off in ft 

hollow tube; while] According to another account, he 

lined it by holding a rod dose to the sun. M A fairy 

ider will say ; and certainly one feels (hat 

the ancients, having looked at the difficulty, simply told a 

pretty tale and paoood by on the other side. 

All the chemical methods of producing fire, those, 
namely, which are now employed, are comparatively new, 

and up till alxuit a century ago, only what we might call 

mechanical methods were available Friction, for example, 

« rybody knows, produces heat, and one of the oldesi 

3 o\' producing tire consisted in rubbing one stick 

against another until the wood inflamed. In some primi- 
tive tribes a -tick was pushed backwards and forwards in a 
)Ve in a piece of wood; sometimes the one stick was 
as a drill, and was rapidly rotated in a hole cut out 

fixed block. Evidence of the extraordinary dexterity 

with which these lire-sticks can he manipulated by Bava 

und in Captain Cook's description of the production 

re among some Australian tribe-. lie writes: M To 

they take two ; ofl wood. 01 

to inches long, the other flat ; the stick 

the] into so obtuse point at one end, and pressing 

it upon the other, turn it nimbly by holding if between 

both their hand-, Afl we do a chocolate mill, often shift - 

hand- up and then moving them down upon it, 

to increase the pn u much as possible. By this 

method th» •• in less than two minutes, and from 

the smallest spark they increase it with great -peed and 

How we should grumble nowadays if we had 

ork hard far two minutes before getting a light ! The 

thai the savage would beat the civilised man 

ll!) 



HOW FIRE IS MADE 

at this game, and we moderns would probably require 
much more than two minutes to produce fire with these 
primitive appliances. 

Another elementary way of making fire is to strike 
flint and steel together, allowing the sparks which are 
thrown off* to fall among some easily-ignited material 
such as tinder. This latter substance consists of the 
element carbon in a finely-divided condition, and is 
obtained by charring fragments of linen. The tinder, 
although it is not actually inflamed by a spark, glows 
with sufficient heat to ignite sulphur -tipped wooden 
splints — " spunks," as they used to be called. 

The flint and steel method of obtaining fire for 
domestic and other purposes was known to the Greeks 
and Romans, and was the one commonly in use in most 
countries up to the end of the eighteenth century. Even 
the inhabitants of such an out-of-the-way place as Tierra 
del Fuego have for centuries been accustomed to get 
fire in this way, only instead of steel they used pyrites — 
a mineral compound of iron and sulphur. It appears, 
in fact, that this mineral got its name from the use 
which was originally made of it in this way. Both flint 
and pyrites received the name of " fire-stone " (Greek 

Another curious device which may be employed in 
making fire depends on the fact that if air is suddenly 
compressed, heat is produced. A simple instrument 
based on this principle and known as a "fire-syringe" 
or a "pneumatic tinder-box" is to be found in any 
list of scientific apparatus. It consists of a glass tube 
fitted at both ends with brass caps, through one of 
which moves a rod with piston attached. If a piece 
of tinder is put in the bottom end of the tube, and the 

120 



HOW FIRE IS MADE 

air in the tube fa compressed by rapidly pushing down 
the piston, the tinder ignites. A similar apparatus, 
with a tube, however, o\' hard wood or ivory, has actually 

> found in use in Bnrmah. 

Among the mechanical methods of producing \nv we 
must not foigei to reckon the lens or burning-glass, 

by which the rays of the sun may he foctl8Sed at a point. 

bustible material which will not ignite when merely 
exposed to the sun will at once take fire if brought to 
the point at which the heat i> thus concentrated The 
burning-lens was known to the Greeks, and is commonly 
by the Chinese. Some readers may remember the 
story according to which Archimedes, during the siege 
Syracuse, weA the Roman licet on fire with the aid of 
burning- It is rather a te w t .* 1 1 1 story, not con- 

firmed by the historians, but it serves at leasl to show 

that the ii^c of the lens in the production of fire was 
familial- to the ancient world. 

All tfa ting methods of obtaining fire are physical 

or mechanical method-, and it was not till 1805 that an 
ide to employ a chemical method for the 

purpose. In that year i certain Frenchman showed that 

splints of wood coated with sulphur and tipped with a 

mix* chlorate of potash and sugar would ignite 

when brought into contact with sulphuric acid —oil of 
vitriol, a- it i- commonly called. The chemical action 

which take^ spontaneously between the acid, the 

chic potash, and the sugar is accompanied by the 

evolution of so much heat that ignition takes place, the 
sulphur firs! and then the wood bursting into flame. 

Tie tir-t really practical lueifer matches irere made 
in England abo I l v They consisted of wooden 

spill with sulphur, and 

181 



HOW FIRE IS MADE 

tipped with a mixture of sulphide of antimony, chlorate 
of potash, and gum. They were ignited by being drawn 
between two folds of glass paper tightly pressed together, 
and a piece of this paper was supplied with each box. 
These matches required much pressure for ignition, and 
as they were liable to throw off sparks, they required 
careful handling. A shilling per box of eighty-four was 
the price, and it is instructive to compare this figure 
with the cost nowadays, when we can get as many as 
four hundred for a penny. 

The great modern development of the match industry 
began with the introduction of phosphorus. This element 
was discovered and its properties were known long before, 
but its application in the manufacture of matches began 
in the thirties of last century. 

Phosphorus in the ordinary condition is a wax-like 
substance which melts at 111° Fahrenheit, and takes fire 
very readily just above its melting-point. It is, in fact, 
this property of very ready ignition which makes phos- 
phorus valuable in the manufacture of matches. The 
slightest friction will cause it to catch fire, and hence 
if a splint of wood tipped with some mixture containing 
phosphorus is rubbed against a rough surface — for example, 
sand-paper — it will ignite immediately. The ignition is 
much facilitated by mixing the phosphorus with an 
oxidising agent, that is, a substance which contributes 
to the combustion of the phosphorus by supplying it 
with oxygen. Saltpetre, chlorate of potash, and red 
lead, which all contain a high percentage of oxygen, 
are the substances chiefly used for this purpose. In 
addition to these two essential constituents of a match- 
tipping mixture, namely, the phosphorus and the oxidising 
agent, there are also binding ingredients, generally glue, 

122 



HOW FIRE IS MADE 

colouring matters, such as ultramarine or vermilion, and 
gritty material, such as powdered glass or fine sand, the 
ed of which is to increase the susceptibility of the 
mixture to friction. 

In order that the splint might be sure to catch when 
the match was struck, it was at one time customary to 
dip it in sulphur before tipping with the phosphorus 
mixture. The combustion of the latter lasts only a 
moment : the sulphur, on the other hand, burns slowly, 
and allows a little more time and opportunity for the 
wood to catch. >ulphur-coated splints are out of date 
HOW, and are met with only in cheap matches of con- 
tinental manufacture. Instead of sulphur, paratlin is 
frequently used : it acts similarly as a go-between for 
the explosive mixture at the tip and the wooden splint. 

The use oi' ordinary phosphorus in matches has many 

dvantages. Their dangers have been impressed on 

many of us by "The Dreadful Story of Harriet and the 

Matches/* and their dm has most certainly led to numerous 

fires. In addition to this objection, there is the fact that 

phosphorus i> poisonous. Workers in match lactone , 

who are exposed to the vapour of phosphorus, are liable 

rinful and often incurable disease of the jaw-bone. 

In the earlier periods of the manufacture of phosphorus 

matches there v Iderable mortality from this Cause, 

but it b found that when close attention i- paid 

to ventilation and clefenliness the danger is exceedingly 

dight. 

XI £kms to the use of ordinary phosphorus can, 

hou< in snother way. Curiously enough, 

phosphorus i- an etemenl which exists in two forms. 
Ju- actor nay represenl two differenl characters 

inthesann play , so phospho pale yellow, 

l IS 



HOW FIRE IS MADE 

waxy solid, very poisonous and very easily inflamed ; at 
other times it is a red powder, not poisonous, and much 
less readily ignited. Regarded superficially, these two 
substances are absolutely different, but they are really 
the same element in different garb, and chemists have 
found a way of changing yellow phosphorus into red, or 
red into yellow. This matter has already been discussed 
at length in Chapter V. 

Soon after red phosphorus was discovered, it was sug- 
gested that the disadvantages of using the ordinary yellow 
phosphorus in matches might be avoided by substituting 
the red form, on account of its being non-poisonous and 
less readily inflamed. Attempts were accordingly made 
to tip matches with mixtures containing red phosphorus, 
but these were not very successful. A certain Swede, 
however, ultimately proposed that, instead of putting the 
red phosphorus at the end of the match, it might be put 
on the surface on which the match was to be rubbed. 
This idea was worked out with complete success, and has 
led to what are now known as " safety matches." These 
matches will not ignite with ordinary friction on a rough 
surface ; they will strike only on the prepared surface on 
the box, consisting very generally of red phosphorus, 
gum, and powdered glass. In order still further to 
diminish risk of fire, the stems of safety matches are 
frequently soaked in some chemical, such as alum or 
magnesium sulphate, so that when the burning match 
is blown out the wood immediately ceases to glow. A 
splint of ordinary dry wood, on the other hand, will con- 
tinue to glow for a little after it has ceased to burn. 
This the reader can easily verify for himself. 

The number of matches manufactured nowadays is 
enormous. It is estimated that in England alone, 300 

124 



HOW FIRE TS MADE 

millions are turned out daily, and that for each million 
of matches about one pound of phosphorus is required 
The forty or fifty torn of phosphorus annually used in 
England for tipping matches arc obtained from bones, 

which contain a large proportion of phosphate of lime. 
The high rate at which matches are turned out has 
become possible only by the introduction of ingenious 
labour-saving machinery, and no one who has not been 
through a match factory can realise how much is done in 
this direction. 

Another curious device for the production of lire was 
brought out bv Dobereiner in 1823. The lamp known 

by his name is no longer used, but it was based on a very 

interesting principle, and therefore d e s er ves consideration* 

We have seen that hydrogen i^ a combustible gas, and 

if we bring a light close to a nozzle from which hydrogen 
ing, it will take fire; that is, the hydrogen com- 
bines with the OXygen of the air at a high temperature, 

water vapour. At ordinary temperatures, on 

the Other hand, hydrogen and oxygen an- gem-rally in- 

differenl i other. There i-, however, one substance 

which i- able to promote the union of hydrogen and 

-n under these conditions, uamelj spo 

platinum — that i», platinum in a wry finely-divided con- 
dition. Platinum i^ usually a compact white metal, 

old, but by special chemical treatment it 

U- obtained as a dark, porous powder, and in this 

iition it i- extremely active If instead of bringing 

•o the nozzle from which hydrogen is issuing, w<- 

hold a little spongy platinum in the gas, tin- natal begin- 
to glow and pre s ent lj the hyd itches lire. 

\ rery pretty instance this of what is tenon n tta- 

lvtic"" action, a him d. noting the curioi, efled which 



HOW FIRE IS MADE 

some substances have in promoting a chemical action 
without themselves being altered thereby. The platinum, 
for instance, which induces the hydrogen and oxygen to 
combine so readily, is found to be unchanged at the end, 
and this is the case also in other processes where finely- 
divided platinum behaves as a catalytic agent. Its action 
has evidently something to do with the very large surface 
which is exposed by the porous, finely-divided metal, but 
opinions differ as to the correct explanation. Some think 
that the gases condense in the surface of the platinum, 
and are thus brought into closer contact — the platinum 
surface acting as a sort of birdlime for the flying mole- 
cules ; others consider that the platinum first lays hold 
of the oxygen molecules to form a compound, and then 
meekly delivers them over to the hydrogen, with the net 
result that water is formed, and the platinum is left as 
it was at the beginning, with nothing to show for its 
labour. 

Although Dobereiner's lamp has gone out in more 
senses than one, there are some modern devices based 
on the same principle. Many incandescent burners used 
to be provided with a little piece of platinum above 
the jet, so that when the gas was turned on, it would 
light without the help of a match. This arrangement 
has gone out of use now, largely because the platinum 
rapidly deteriorates in efficiency and finally loses its 
power of igniting the gas. 

Another piece of apparatus, based on the same 
principle, is a cigar-lighter which is sold at the present 
time. This consists of a small metal vessel provided 
with a cap ; the vessel holds some volatile spirit, and 
attached to the cap there is a piece of very fine platinum 
wire. When this is held in the vapour of the spirit, 

]26 



HOW FIRE IS MADE 

while air has access to the vessel, the spirit combines 
with the oxygen under the influence of the platinum, 
heal is produced, the platinum glows, and finally the 
spirit bursts into flame. 

Reference hasjusl been made to the very high cata- 
lytic power of platinum when it is in a finely-divided 
condition. Generally speaking, it may be said thai 
finely-divided matter behaves differently in many respeci 

i compact matter of the same kind. Jt is, for 

nple, a consequence of the law of gravitation thai 
solid particle^ in the air Boon tall bo the ground, bu1 
it* they are infinitesimally small they may travel quite 
■ long distance without coming to earth. Thus the 

itiful sunsets seen in England in 1888 were attri- 
buted to the presence of very fine dust in the atmos- 
phere, carried all the way from a volcanic eruption on 

the other side ot' the globe. 

Iii also u> combustion finely-divided substances 

inewhal peculiar manners, Everybody would 

regard iron and lead as dements of the most staid and 

r temperament : and yel it i^ possible to obtain 

t tte of Mich tine division, thai when 
they are thrown OU1 of any vessel into the air, the] 

f their own accord. The finely-divided sub- 
ivlati\elv a much greater surface than the 

I substance, and t h of nisi ing or oxida- 

tion i> thereby so much i, I that incandescence i 

1 ; the | ►mbii-tion, which is slow under 

ordinary conditions, b iptdL The pheno- 

■ scribed ;>~ u ipontaneoufl combustion," 

but iei should dearly understand thai the cheuri- 

which take place when finely divided iron 

I take tii* in air 't\ the am hen 



HOW FIRE IS MADE 

they rust ; the only difference is that the latter change 
is spread over a much longer time. 

There are other cases in which combustion appears 
to take place without any obvious cause, and to which 
the term " spontaneous n is applied. Stacks of hay 
occasionally take fire of their own accord, and heaps 
of cotton waste or rags impregnated with oil have been 
frequently found to exhibit a similar behaviour. But 
however " spontaneous " the occurrence may seem to be, 
there is in each case a sufficient reason for the combus- 
tion. In the first case the hay has been stacked while 
still moist, and in these circumstances fermentation sets 
in. Now fermentation is a chemical change of the con- 
stituents of the hay, promoted by the presence of minute 
organisms, and this change, like most chemical reactions, 
is accompanied by the evolution of heat. If the hay 
were lying out in the open, this heat would be dissi- 
pated at once, but in the inside of a stack it cannot 
escape so easily ; it accumulates more and more as the 
fermentation process goes on and ultimately the tempera- 
ture rises so high that the hay takes fire. 

The explanation is different in the case of the oily 
rags or cotton waste. Many oils are readily oxidised 
by the oxygen of the air, and when such oils are spread 
over the extensive surface of rags or waste the oxidation 
takes place very rapidly. The rags and waste being 
bad conductors, the heat generated in the oxidation is 
rapidly accumulated, and finally leads to the so-called 
" spontaneous combustion. " 

In both these cases the chemical change involved is 
a slow combustion at the beginning, and becomes rapid 
at the end only because the heat generated in the pro- 
cess has been unable to escape. With rising tempera- 

128 



HOW FIRE IS MADE 
hire ■ chemical change invariably becomes quicker and 

quicker, hence as the heat accumulates in the hay or 

the cotton waste, the chemical forces become more ami 

more impetuous ami ultimately lead to a general con- 
flagration. The affair, in tact, resembles the accumula- 
tion of money at compound interest. 

Hay>tacks are not the sort of' thing that the ordinary 
individual can experiment with, but there i- one very 
simple example of the way in which the heat effect 

inying a slow combustion may be accumulated. 

It' iron filings are mixed with Bawdust and a little water 
i- added, then alter a lew hours steam will be seen to 
come off from the mixture. Now the heal evolved 
during rusting cannot be detected in ordinary circuni- 
stances, but in this little experiment the non-conduct - 
Utwdust allows the heat to accumulate until it is 
obvious to the senses, 

other kind of spontaneous combustion in 
which people believed at one time, namely, the spon- 
taneous combustion of human beings, Jt was supposed 
a living human body might be consumed by fire 
ttaneously generated in the internal organs, In the 
Philosophical Transactions of the Royal Society for 1744, 
for example, one finds a communication to the following 
4 seventeen year- ago, three noblemen, 

lor decency"- Bake I will not publish, drank 

by emulation strong liqu id two of them died, 

tied by a flame forcing itself from the 
widespn I be belief in the possible 

mbustioo of human beings thai ti. 

i thoughl it worth while to deal with the 

I to i« cord his \ ji -w that M while i tit dead 
body charged with alcohol maj perhap burn, ■ living 

i 



HOW FIRE IS MADE 

body in which the blood is circulating cannot take fire 
spontaneously.'" The story of this curious belief shows 
how easy it is, firstly, to make wrong observations, and, 
secondly, even when the facts have been correctly ascer- 
tained, to rush at the first explanation which suggests 
itself. 



130 



CHAPTER XII 
NATURE'S STORES OF 11 EL 

IT is all very well to he able to make lire, hut our 
achievements in this direction would he of little use 
it' Nature did not supply US liberally with combustible 
substances or fuel-. So tar a- combination with oxygen 
and production of heat and light are concerned, a great 
many substances might be called fuels, but the name is 
terally restricted to those which contain the element 
boo in some form, and which are obtained in U 
quantities on or under the surface of the earth. Some 
r efe r en ce ha- already been made to these carbonao 
fuels, but much more remains to be -aid on this inter- 
esting tonic. Hie process of combustion i^ perhaps the 

• fundamental chemical change with which we are 

ited, and to our modern world, with all it- travel, 

industry, and social life, the production and maintenance 

of <i: wential a- air and water are to tin* 

human body. 

I i i sees the fuels supplied by Nature are available 

directly for man*- use without any other than the simplest 
•meiit. Wood and peat, fc d only to be 

cut and dried before the) are in condition for bun, 
while in the I the only n . preliminai 

the cutti to the 

, w,>od, md coal, re pn « nt three 

stag? (aid. Living 

1 n 



NATURE'S STORES OF FUEL 

wood, apart from the large amount of water which it 
contains, consists chiefly of cellulose, a compound of the 
three elements, carbon, hydrogen, and oxygen. If the 
wood dies and is allowed to lie in the soil where it has 
grown, a remarkable series of chemical changes sets in. 
In many cases the fallen forests and jungles of the past 
have been submerged and then covered over with alluvial 
deposits of clay and sand, so that what was once a 
luxuriant vegetation on the surface is now buried many 
feet below. 

Now when wood or any other vegetable matter con- 
taining cellulose is kept below water or in a moist soil, the 
relative proportions of the carbon, hydrogen, and oxygen 
which made up the cellulose begin to change. De- 
composition and fermentation set in, the hydrogen is 
gradually eliminated in the form of marsh gas — a com- 
bustible compound of carbon and hydrogen — and the 
oxygen in the form of carbon dioxide. Any one who 
pokes a stick into a stagnant pool at the bottom of 
which vegetable matter is decomposing will observe 
bubbles of gas rising to the surface. These bubbles have 
been examined by chemists, and are found actually to 
contain carbon dioxide and marsh gas. 

The result of these slow changes — extending over a 
long period — is that instead of cellulose there is left a 
carbonaceous mass containing a very much higher per- 
centage of carbon than the original wood. If the de- 
composition has been going on for a very long time and 
at some depth below the surface, the product is a compact 
coal, containing relatively small quantities of hydrogen 
and oxygen. Vegetable matter of more recent date will 
not have been carbonised to the same extent, and will 
have reached the stage represented by brown coal or 

132 




- 
- 



$2 



o 5. 

•j , A 

-~~3 



P 






NATURES STORES OF FUEL 

lignite. Peat, again, is vegetable matter — chiefly moa — 

which li undergoing decomposition and carbonisa- 

tion far a very mud) shorter time, and which, being cm 
the surface, baa no* been subjected to the same pressure 

and is therefore less compact. 

\ ores will ^how how the amounts of hydrogen 

and oxygen diminish regularly as we pass from wood to 

a hard coal like anthracite. To make the figures com- 
parable, the amount of carbon i- put a- equal to 100 in 
h case. 

Km. Hydrogen. 



d . 


100 


12 


83 


. 


100 


9 


56 


ite 


1 00 


8 


i i 


Bituminous coal . 


100 


6 


si 


Anthracite . 


LOO 


9 


2 



Responding to the gradual alteration in composition, 

ge also in the way these fuels behave when 

irned. For a brightly biasing fire there is 

■ jmthing ]ik< wood, the reason being thai, when it is 

quantities of inflammable gas are given off; h< 

wood catches lire much more easily than the other solid fuels, 

when it ha- ignited it burns with a larger amount of 

flame, for flame is limply burning gas, The inflammable 

en off from heated wood consist to a la 
ut of hydrocarbons — that i-, compounds of carbon 
and hy drogen. Wood, therefore, which has underg 

uid which has in the process Losi the 

grea its hydrogen, will be able to yield little or 

u when beat d. Tak( anthracite, for 

mple — a pedes ot coal which i- largely mined in 

Wales; it coots high proportion of carbon, and 



NATURE'S STORES OF FUEL 

very little hydrogen and oxygen. When heated, it gives 
off* practically no inflammable vapour, and this makes it 
very difficult to ignite ; for the same reason, even when it 
has been successfully ignited, it burns with very little flame 
or smoke. These characteristics make anthracite unsuit- 
able for domestic use; it can be kept burning only in a 
strong draught, and is accordingly chiefly employed in 
boiler furnaces. 

The solid fuels which have been considered in the fore- 
going paragraphs are all directly supplied by Nature, and 
are to be had more or less for the gathering. In this 
little island we pick up over 200,000,000 tons of coal 
every year, and we may well ask how long this will 
continue to be possible. Shall we be able to draw upon 
Nature's stores for an indefinite period ? Is it time to 
consider what we should do if the coal supply of the world 
ran out ? 

Before attempting to answer these questions, we must 
recall the fact that Nature supplies us also with liquid 
fuel, yielding it to us with a very slight expenditure of 
energy on our part. It has long been known that in 
certain countries there were indications of the presence of 
oil in the earth's crust, but it was only forty or fifty years 
ago that a systematic search was made. About that time 
a certain American engineer drove an iron pipe from the 
surface down through the rock, and was surprised to find 
that when the pipe had gone down about thirty-four 
feet, oil rose nearly to the top. He had in fact " struck 
oil." This discovery, of course, led to other attempts to 
tap the subterranean oil stores, with the result that to-day 
whole districts in the United States and Russia — the two 
countries which supply by far the greater part of the 
world's liquid fuel — are given over to "oil-bearing." 

134 




: 



To - ired trolley, fitted wi 

near the blazing borehole, 
lowered. 






NATURE'S STORES OF FUEL 

Sometimes the oil has to be pumped up like water from 
11, hut iu other cases the oil in the internal reservoirs 
is under pressure, and m> soon as an opening is provided 
it spouts out with greal force. 

It mighl be thoughl an easy matter to colled the oil 
which comes up these wells, hut it is frequently very 
difficult, especially when the bearing has just been made, 
and the oil is forced out under prosure. A certain well 
in Baku — the Russian oil-bearing district — tapped in 
1886] began to spout with such vehemence thai the whole 
surrounding country was deluged For a time nothing 

could be done to Stop the outflow, and many thousand 

tons of oil were lost. The greal pressure which sometimes 

ts in the subterranean reservoirs was well shown by 

mother fountain which burst out a few month- later and 

to a height of 850 Beet ; the « cape in this case was 

: that it formed an extensive petroleum lake, and 

overflowed into the Caspian s 

Tin crudi petroleum obtained from the American or 

ian oil-wells must be subjected to chemical treatment 

before it is ready for the market. It is distilled, and the 

volatile portions of the oil are thus separated from the 

portions. Hie reader would he quite surprised 

to find what a number of distinct products can thus 

be d from natural petroleum by the Simple 

of distillation, 

T most volatile portions of the petroleum yield 

naphtha and petrol, the latter substance now largely in 

mil in tlm nf motor cars. The petroleum 

which distil* omewhat higher temperature is 

used for illuminating purposes, and it is j n this form 

of lamp oil that the hulk of the American petroleum 

ulti' be mai I « L After the petroleum 



NATURE'S STORES OF FUEL 

suitable for lighting has been distilled off, there is next 
obtained a heavy oily portion which may be used as a 
fuel or for lubricating purposes, while, last of all, there 
is a residue from which may be extracted such useful 
substances as vaseline and paraffin wax, the latter em- 
ployed very largely in the manufacture of candles. 

Closely allied to the petroleum of Pennsylvania or 
Baku is so-called " natural gas," which, in fact, frequently 
makes its appearance along with the petroleum. From 
the chemical point of view, it is extremely similar to 
petroleum, consisting largely of hydrocarbons ; these, 
however, are still more volatile than the hydrocarbons 
present in petroleum, and are therefore not found in the 
liquid condition. 

In the United States enormous quantities of natural 
gas are obtained, so much so that in many districts the 
manufacture of coal gas for lighting and heating purposes 
is quite superfluous. We do not, however, require to 
travel to the United States to find natural gas. There 
is actually a supply of it in England, although not on a 
large scale. It was discovered in 1893, as a bore-hole 
was being sunk at Heathfield, in Sussex, for the purpose of 
obtaining water. When the boring had reached a depth 
of over 200 feet, no water had been got, but an inflam- 
mable gas issued from the bore-hole. Some three years 
later another boring was made in the same neighbourhood, 
and at a depth of 312 feet gas was met with in consider- 
able quantity. The supply was under great pressure, for 
when ignited it gave a flame 16 feet high. Obviously 
one of Nature's gasometers had been tapped, and since 
then this natural gas has been used regularly in the 
immediate neighbourhood for lighting and heating pur- 
poses to the extent of about 1000 cubic feet per day. 

136 



NATURE'S STORES OF FUEL 

clusively (»!' methane or marsh 

. the simplest oompound of carbon and hydrogen. 

Hie origin of solid fuel has already been discussed 

is fairly evident, bn( il i^> mocfa more difficult to 

:tv the source of all the petroleum which has been 

ined so abundantly during the las( forty y< 

Borne authorities assign to it an inorganic origin, and 

suppose thai the hy dr ocarbons of which petroleum oon- 

i have been produced by the action of water on 

carb substances arc compounds of metals 

with carbon, and are decomposed by water in such a 

that Hie carbon of the carbide forms a new com- 

nd — s h y droc a rbon — with the hydrogen in the water, 

v readers doubtless are familiar with one carbide 

which i- in common use, namely, calcium carbide This 

on contact with water generates acetylene, 

a lr ion which has many advantages a- an illuminat- 

Hirvclc lam))-, for example, are made in which 

is being prepared in the lamp 

iter to drop on Lumps of calcium carbide. 

d that water, penetrating through 

; n the crn-t i nth. ha- acted on subterranean 

abides with the production of petroleum. 
Another explanation, which on the whole ha- more 

gaids petroleum as derived from an organic 

her than • . \< • ording to 

this be animal remains of and* r- 

£oip nge, whereby all nitrogenous and othei mat! 

ntly tb 
being I to distillation by the combined action 

of heat and p: alone, yielded the 

ileum wh 

In ion with all thee fuel aipplie 



NATURE'S STORES OF FUEL 






petroleum, and natural gas — a question of the utmost 
importance arises, to which reference has already been 
made. We are using up these fuels at an enormous rate, 
and there is no reason to suppose that the stores are being 
replenished at anything like the rate at which they are 
being consumed. In this respect we are, in fact, living 
on our capital, and, moreover, we do not know what is its 
amount. Estimates have indeed been made of the probable 
duration of our coal supplies, and Royal Commissions have 
dealt with the subject. The authorities are divided, but, 
on the whole, it seems we may reckon on our coal lasting for 
the matter of five hundred years or thereabouts, even when 
allowance is made for the probable increase in the con- 
sumption. It must be remembered also, for our comfort, 
that new coalfields are occasionally discovered, as was the 
case recently in the county of Kent. The Kentish collieries 
mean a substantial addition to our coal capital, and they 
may outlast the older ones in the north, so that some day 
it may be necessary to carry coals even to Newcastle. 

Estimates like the foregoing are based on the actual 
inspection of the seams of coal which have been dis- 
covered, their thickness and extent, but who will be bold 
enough to say how long the subterranean reservoirs will 
keep us supplied with oil and gas ? Human eyes have 
never seen, nor ever will see, what these hidden reservoirs 
contain. As a matter of fact, signs are not wanting 
that the stock of petroleum and natural gas is beginning 
to run short. The output of oil, it is true, is increasing, 
but this is due, not to any natural increase given by 
the existing wells, but to an increase in their number. 
The oil-yielding wells are very short-lived, and as new 
ones are continually being opened, the available oil-fields 
will soon be entirely covered. 

138 



NATURE'S STORES OF FUEL 

We must not forgel to include in our fuel capital the 
vast stock of timber on the surface of the globe, and the 
enormous quantities also of peat found in many count] 
Hnw far may are regard these as reliable sources of fuel? 
Wood, is, of course burned in many countries where there 
is a large extent of forest, but it would be absolute 

madness to use up all our timber in this way. It is the 

tation of the world which, as we shall see, i^> the 
necessary counterpart of animal lite, and gradually to 

CUt down all the forests on the face of the globe would 

be a suicidal policy. Besides, there is a Urge demand for 
timber for architectural and constructive purposes, and 
even as matters are at present, tin 1 forest-covered land of 
\ rth America and Europe is being laid bare at a rapidly 
incp tte. Trees do not grow in a hurry, and once 

the primeval forests are cut down, the keeping up of a 
supply of timber by planted trees is hardly feasible. 

And what about peat ? In Ireland alone there are 

1,000,000 acres of peal bogs, and it is estimated 
that an 4 a bog of an average depth of even 8 

would yield about 1260 tons of dried peat. In 

B ia there are about 100,000,000 acres of bogs, -<> 

that altogether the fuel stored up in the form of peal 

must lx* v« ry considerable What militates againsl the 

u a fuel is the \ery large amount of moisture 

which it holds. When freshly dug if may contain as 

much as ' (i . cent, of water, and the problem is 

how | ijd ( ,t this and obtain the fibre of the 

ondition fit for burning. The usual method 

to air until it is (\)\ requires 
much time and It is further i verj bulky fuel, 

and. m ing to fl>. ■ lie output of p at 

has than sufficed for local de- 

L39 



NATURE'S STORES OF FUEL 

mands. In recent years, however, great advances have 
been made in the utilisation of peat. Methods have been 
devised of squeezing out the water by mechanical means, 
and compressing the combustible fibres into briquettes ; 
these are not only more compact than the air-dried peat, 
but have also a higher heating power. 

It is conceivable that in the distant future of the 
world's history there may come a time when, apart from 
timber, the natural stores of fuel — coal, peat, petroleum, 
and natural gas — are completely or almost exhausted. 
What then ? 

Necessity is the mother of invention, and we may be 
sure that before things shall have come to such a pass, 
the ingenuity of man will discover a way out of the 
difficulty. As a matter of fact, there are already indica- 
tions that alcohol is to be the fuel of the future. In the 
form of methylated spirit it is used to a very small extent 
at the present day, but it looks as if it were to survive 
as a fuel when all others have gone. When every oil- 
well is dry, when a piece of coal can be seen only in a 
museum, and when the peat bogs are no more, then 
alcohol, if no better substance has been discovered in the 
meantime, will come to its own as a fuel. 

" All very nice," the reader may say, " but how is the 
alcohol to be produced in the large quantities which will 
be necessary ? " By the simple and time-honoured opera- 
tions of growing potatoes, wheat, rice, beetroot, and 
similar substances. From these alcohol may be obtained 
by fermentation, as will be shown in a future chapter. 
To those who doubt whether alcohol could be used as 
fuel, say in driving an engine, the best reply is that the 
thing has been done. Experiments have shown that 
alcohol can be employed with satisfactory results in place 

140 







round i he I 
up to the height of fifteen lo 
bas been use 



NATURE'S STORES OF FUEL 

of petrol, and it has certain advantages over the latter 
fuel, such as greater safety in handling. At presents 
while the natural fuel is bo abundant, the price of 

alcohol will prohibit its general use as a fuel; but it 
: least a comfort to know that we have something 
promising in reserve. 



141 



CHAPTER XIII 
MORE ABOUT FUEL 

IN the foregoing chapter we have discussed the various 
natural fuels which are available for use without any 
more than a slight preliminary treatment. There 
are, however, other substances commonly classed as fuels 
to which no reference has yet been made — for example, 
charcoal, coke, and coal gas. Although these substances 
are to be regarded as fuels, they do not belong to the 
same category as wood, peat, coal, or petroleum. Unlike 
the latter fuels, they are not obtained directly from 
Nature ; they are produced secondarily from the natural 
fuels by special treatment. 

Generally speaking, the secondary fuels, charcoal, coke, 
and coal gas, are obtained by the process of destructive 
distillation. This operation sounds rather alarming, but 
it is one which most boys have performed on a small scale, 
and the principle of it is comparatively simple. In 
ordinary distillation, where a liquid is converted into a 
vapour, and this vapour is condensed by passing through 
a cooled tube, any products obtained in the distillate 
were already present in the original liquid. The pro- 
ducts, however, of a dry or destructive distillation are 
not present as such in the original substance ; they are 
only produced by its chemical decomposition. 

The little experiment in destructive distillation which 
many readers have probably made consists in filling the 

142 



MORE ABOUT FUEL 

bow] of a day pipe with little bits of coal, blocking up 
the mouth of the bowl with day, and then heating it in 
a fire. When this is done, a gas will be found issuing 

from the end of the pipe stem, which will burn with a 

luminous flame. This gas is essentially the same as coal 

I the method by which it has been obtained is 

destructive distillation — the process by which also char- 

tke, ami coal gas arc obtained from the natural 

It i-. of course, necessary that the natural fuel? 

which are undergoing destructive distillation should be 

i from contact with air during the process — other- 

OOmbustion would take place. What occurs then 

is that the carbon compounds in the natural fuel are 

chemically decomposed by the action of heat : the atoms 

of carbon, hydrogen, and oxygen are re-arranged, and 

product- air formed which did not exist a- such in 

the original fuel. 

be chemical decomposition which takes place in the 
dry distillation of wood or coal is exceedingly complex, 
and the number of products that can ultimately be 

f large indeed. Hut although this u 
the first crude products are only four in number, namely, 
watery liquid, tar, and ie-idiie, these differing in 

cording a- wood or coal i- being subjected to 
distillation. 

In th» »f wood the pn < carried 

out ' od, burning pari of it, and u 

i obtained to decompose the rest. Tin- i a 
method, a i mosl of the produci - are i 

for no provision i^ made to catch those which 
The residue Lb known i i »al. and 

U boo, with -mall quantities of 
and QltrOgl ii. and a little I fa OT 

I 1 I 



MORE ABOUT FUEL 

mineral matter. Such a primitive method of converting 
wood into charcoal is frequently replaced by a more 
scientific procedure, in which the wood is heated in closed 
vessels or retorts, and provision is made for collecting or 
condensing any volatile matter. 

In considering the use of wood as a fuel, we have seen 
that its ready combustibility is due to its giving off in- 
flammable vapour. It is therefore not surprising to find 
that when wood is heated out of contact with air a 
quantity of gas is obtained. The main constituents of 
this gas are carbon dioxide, carbon monoxide, and marsh 
gas ; the two latter are combustible, and although the 
gas has not much illuminating value, it may be used to 
heat the retorts. This is a simple example of the way in 
which the by-products of a manufacturing operation may 
be utilised so as to diminish the cost of production. 

The volatile matter obtained by subjecting wood to 
dry distillation not only yields a combustible gas, but 
condenses partly to a tar and partly to a watery liquid. 
The latter yields acetic acid — the acid of vinegar — and 
wood spirit ; this consists largely of methyl alcohol, and 
is added to rectified spirits of wine in order to produce 
methylated spirit. The object of thus "denaturing" 
ordinary alcohol is to provide a spirit which may be 
employed for industrial purposes, and which, at the same 
time, is not drinkable. Whether the latter condition is 
fulfilled is doubtful, for it is said that such methylated 
spirit is consumed as a beverage, to the injury of the 
revenue. Accordingly, the bulk of methylated spirit now 
sold has a small admixture of mineral naphtha or light 
petroleum to render the taste more objectionable. 

When coal is subjected to destructive distillation the 
effects are in general the same as those obtained with 

144 



MORE ABOUT FUEL 

wood, but thf character of the products differs in some 
important particulars. Hie gas which is given off on 
heating coal is of much more use tor illuminating pur- 
poses, and is, in fact, after purification, nothing else than 

the common coal gas used throughout our towns. This 

data largely oi' hydrogen and marsh gas, together with 

some carbon monoxide and small quantities of heavy 

hydrocarbons which are responsible for the illuminating 
or. 

In the crude gas which comes from the retorts there 
are several undesirable constituents which must be 
removed before the gas can be supplied to the public. 
In addition to carbon, hydrogen, and oxygen, coal 
contains small quantities of the elements nitrogen and 
sulphur, and these appear to some extent in the coal 
in the form of ammonia — a compound of nitrogen 
and hydrogen — and sulphuretted hydrogen — a com- 
pound of sulphur and hydrogen. The ammonia coll> 
mostly in the watery liquid, which accordingly becomes 
wBcatmty in contrast with the add watery liquid obtained 
in the destructive distillation of wood. The last ti 
of ammonia are removed from coal gas by u scrubbers 91 — 

towen packed with coke or brushwood over which a 

tant stream of water is trickling. The current of 

8 in the opposite direction, and as ammonia 1 

soluble in water, it is all removed before the gas 
top. 

The sulphuretted hydrogen resulting from the above 
process, if it were allowed to remain in the coal 
would on burning produce sulphur dioxide, and this, 
in anything more than a small quantity, would b 
very objectionable addition to the atmospl, The 

gas idingly passed through i of purifi 

1 to I 



MORE ABOUT FUEL 

containing slaked lime and iron oxide. The reader is 
already familiar with the first of these as being an 
alkaline substance, in virtue of which it readily absorbs 
anything of an acid nature which passes through the 
purifiers. Now both carbon dioxide, a little of which 
is sure to be present in the gas, and sulphuretted 
hydrogen are substances of an acid nature, and one 
would therefore expect them to be fixed by the lime. 
Sulphuretted hydrogen, however, is not absorbed by 
lime when it is mixed with carbon dioxide, so in order 
to insure the complete removal of the former the coal 
gas must also be passed over iron oxide. This substance, 
generally in the form of Irish bog ore, is at first very 
active in holding back the sulphuretted hydrogen, but 
as it absorbs more and more it gets exhausted, being 
gradually converted into sulphide of iron. A course 
of fresh air, however, is found to have a beneficial effect 
on its activity, hence the exhausted or "spent" oxide 
of iron is taken out of the purifiers and spread on the 
ground for a time. During this " rest cure " the sulphide 
of iron enters into a chemical reaction with the oxygen 
of the air, with the result that the element sulphur is 
liberated and iron oxide is re-generated. The material 
is then again capable of actively absorbing sulphuretted 
hydrogen, and is therefore returned to the purifiers until 
exhausted a second time. This process of " revivifying " 
the iron oxide may be repeated a good many times until 
the material has picked up about half its own weight 
of sulphur. It will then have lost its effectiveness as 
a purifier of coal gas, and is accordingly sold to the 
sulphuric acid manufacturer. As the proportion of 
sulphur in the original coal is not more than one or 
two per cent., this is a very instructive instance of the 

146 



MORE ABOUT FUEL 

value of gathering up the fragments : even the very 
impurities in the coal gas are made to contribute to 
the cost of its production. 

Thi> remark covert also the ammonia which is found 
in crude coal gas. As has been stated already, the 

destructive distillation of coal converts some of the 
nitrogen which it contains into ammonia, and this has 
turned out to he a very valuable by-product of coal- 
manufacture. From the watery liquid, in which 
it mostly collect-, the ammonia is driven out by a current 

steam; it is then passed into sulphuric acid forming 
sulphate of ammonia, and the crystals of this substance 
are fished out from time to time. On the average, a 
ton of coal yields l 20 lbs. of ammonium sulphate ; the 
latter substance fetches a good price as a manure — 
about I'M) per ton — and it makes, therefore, a very 
substantial contribution to the expense of producing 
the coal gas. 

Other by-products obtained in the manufacture of 
coal gas are tar and coke. From coal tar so many 
interesting and useful substances are prepared that a 
ial chapter must be de\oted to their consideration, 
wIil: rcn from this uninviting and 

unpromising matt-rial many beautiful product* may be 
extract- 

<ke i- tlu- residue in the (etorb after all gas, tar, 

and ammonia haw been driven off The mineral matter 

in the J coal i> not \olatile. s ( , that it 

sins in the coke, which contains about ninety per 
cent, of carbon and small quantitiei of hydro 

--en, nitrogen, and sulphur. G used 

fuel, although the reader will understand that nnce the 

volatile tible ga -e have I, it i rather 

147 



MORE ABOUT FUEL 

difficult to burn. In domestic use it must be mixed 
with coal, but in furnaces where there is a powerful 
draught, it is very satisfactory by itself and gives oft* 
no smoke. Large quantities of gas c'oke are employed 
in lime and cement-burning. 

Such are the chief products of the destructive distilla- 
tion of coal in the manufacture of coal gas. As a fuel, 
coal gas, if not particularly cheap, is comparatively clean, 
and certainly very convenient. Hitherto it has been 
used principally for lighting purposes, and we can best 
appreciate its convenience in that respect from the 
standpoint of our great - great - grandfathers. What 
seemed to them the marvel about coal gas was that no 
wick was required as in the lamps and candles with 
which they were familiar. So marvellous did they find 
it, that it was regarded as rather uncanny, and the 
lighting of gas lamps was at first thought to be a 
perilous undertaking. 

Nowadays, electricity is a competitor with gas as an 
illuminant, but the latter is being increasingly employed 
as a fuel, and may be said to hold its own. In England 
there is a decided preference for the old-fashioned, cheery 
open coal fire, with all its accompaniments of ash, soot, 
and smoke ; there is little doubt, however, that the 
gas fire or stove is gradually coming into favour on 
account both of its cleanliness and its convenience. In 
estimating the chances that coal gas will hold its own 
with electricity as a lighting and heating agent, the 
very important part played by the by-products of the 
gasworks must not be forgotten. Here, as in so many 
cases, it is the by-products which settle the question 
whether a given manufacture will pay or not. 

Coke, which has been referred to as a by-product in 

148 



MORE ABOUT FUEL 

the manufacture of coal gas, is prepared in large quan- 
tities for its own sake. It is extensively Used in metal- 
lurgical operations, that is, in the production of metals 
from their ores. The coke required for this purpose must 

specially dense, and as free as possible from sulphur 

and ash. Gas coke does not adequately fulfil the>e 

conditions, and in Great Britain as much as twelve million 

J are destructively distilled every year in 

ial ovens in order to get coke suitable for metal- 
lurgical purposes. This is frequently described as oven 
coke. 

He use of coke in metallurgical operations is readily 
understood. In iron-smelting, for instance, the ore 
consists mainly of iron oxide, and when this is heated in 
the bla^t furnace with coke, the oxygen prefers to be in 
partnership with the carbon rather than with the iron, so 
the latter is liberated, and is obtained from the 
blast furnace as molten metal. 

•al i-> not the only naturally occurring substance that 
bjected to d< ^tractive distillation. In Scotland there 

is a virv considerable industry founded on the winning of 

fuel oil by the destructive distillation of shale. This 

Mice which differs from coal in that it 

I much larger proportion, sometimes 

much as ~ ( > per cent., of mineral matter or ash. By the 

distillation of a ton of shale about thirty 

gallon- of - obtained, which by further 

tment is made to yield paraffin oil, lubricating oil, 
and paraffin 

made also bo subject peat to de- 

<*tru« filiation, but tin- generally ended in 

failure. The difficult* . are no* being over- 

lid quite recently a promising development ha- 
ll!) 



MORE ABOUT FUEL 

taken place in South Germany, where a plant has been 
put down beside an extensive peat bog, and is turning out 
tar, paraffin, ammonia, and coke. If this process should 
be found commercially sound, we may yet see the peat 
bogs of Ireland being converted into productive ground, 
while at the same time a new industry will be available 
for the people. 

Leaving out of account for the moment the tar, ammonia, 
and sulphur obtained as by-products in the destructive 
distillation of coal, we may regard the net result of the 
operation as giving us for fuel coke coal gas instead 
of coal. Now whereas coal is an exceedingly dirty fuel, 
both coke and coal gas are clean fuels, burning without 
smoke. Bearing this in mind, we might ask the question 
whether it would not be possible to modify the destructive 
distillation of coal in such a way as to obtain a coke-like 
product, which would, however, still retain enough gas- 
producing material to make it readily inflammable, and 
which would at the same time be a smokeless fuel. 
Experiments made during the last four or five years have 
shown that this is possible when the temperature of the 
retorts, instead of being raised to 1600° or 1700° 
Fahrenheit, as is usual in gasworks, is kept about 800°. 
The quantity of gas given off during the heating is not so 
large, but the half-coked coal left in the retorts, contain- 
ing as it does a certain proportion of volatile matter, is a 
smokeless, easily ignited fuel. This product is now on 
the market under the name of coalite. 

The convenience of gaseous fuel for many purposes has 
stimulated efforts on the part of chemists to convert 
carbon entirely into combustible gaseous products. It 
was discovered long ago that when a current of steam is 
passed through red-hot carbon, an inflammable gas is pro- 

150 



MORE ABOUT FUEL 

duced. The chemical reaction involved is very simple ; 
the water is decomposed by the red-hot carbon, and the 
latter appropriates the oxygen, forming carbon monoxide. 
The hydrogen of the water is left in the tree state, and 
i^siie^ from the furnace along with the carbon monoxide. 
Since both these pises are combustible, the reader will 
perceive that the simple passage of steam over red-hot 
carbon means the conversion of a solid into a gaseous 
fuel. The product is called M water gas/' a term which 
must be carefully distinguished from "water vapour"; 
the latter is of course not combustible. 

Simple as the foregoing process may seem to be on 
paper, many difficulties were experienced in making it 
work on a large scale. The decomposition of steam by 
earlxmaceous fuel requires a large amount of heat, and it 
'i found impracticable to supply this by external 
heating of the retorts containing the coke or coal. The 
device was accordingly adopted of heating the fuel inter- 
nally by it- partial combustion. Air is blown into the 
1 1 containing the ignited fuel, which is raised to 
incande>cence by the heat given out in its own com- 
bustion : th< Miis condition is attained, the 
air bla-t is shut off and -team is blown into the retort. 
The formation of water gas at once begins, and is con- 
tinued until the tem p erature Galls below ;* certain limit, 
when tl DO blast IS shut off and air is once again 
blown in. It must be unders to od that the two parts of 
tin's operation, the air blow and the steam blow, are 

iiy to each other, the heal evolved in the 

first _ supplying the energy required in the second 
_ce. 
W his mixture of hydrogen and carbon 

mo! .nil- with a non-luminous Same, and, if it i- 

Ml 



MORE ABOUT FUEL 

to be used for illuminating purposes, must either be 
carburetted — that is, provided with hydro-carbons to 
render its flame luminous, or used with incandescent 
mantles. In America water gas is frequently used in 
place of coal gas ; in this country it is never supplied 
alone for lighting purposes, but is often mixed with coal 
gas. One objection to its use is the excessively poisonous 
nature of carbon monoxide, referred to in a previous 
chapter. On this ground it is considered unsafe to dis- 
tribute to the public coal gas which contains more than 
about 16 per cent, of carbon monoxide. 

Has the reader ever realised what an enormous amount 
of energy is stored up in a pound of coal, or a cubic foot 
of coal gas ? When the fuel is burned this latent energy 
becomes manifest in the form of heat, and it is actually 
found that the heat given out when one pound of coal is 
burned would be sufficient to raise the temperature of 
seven tons of water 1° Fahrenheit — say from 60° to 61°. 
Now heat is convertible into other forms of energy, and 
may, for example, be transformed into mechanical energy ; 
thus it has been shown that the quantity of heat which 
would raise the temperature of one pound of water from 
60° to 61° would, if converted into mechanical energy, 
be able to raise a weight of 772 pounds through 1 foot, 
or, what is the same thing, a weight of one pound through 
772 feet. By means of this mechanical equivalent of 
heat, as it has been called, some one has calculated that 
if the energy latent in one pound of coal were converted 
without loss into mechanical energy, it would do as much 
as five or six horses working for an hour. 

But one must admit that this is quite an ideal process. 
Even in the best engines we can employ to convert the 
latent energy of fuel into mechanical energy only a 

152 



MORE ABOUT FUEL 

portion of the beat reappears in the form of useful work. 
In thi^ respect the internal combustion engine, sucb as 

i> used on a motor car, is much superior to the steam 
engine, bj which we convert only about 10 per cent, of 

the heat value of the coal into power. 

The power of different fuels to give out heal when 

burned — the calorific power, as it is called — varies very con- 
siderably. The heat given out in the combustion of one 
(1 of coal, for example. is nearly twice as great as 

that liberated when one pound of dried wood is burned. 

The calorific power of petroleum, on the other hand, 

i> nearly SO per cent, greater than that of coal. In 

cting a fuel, however* many other factors have to 

be borne in mind beside- the calorific power; the prudent 

Heer ha- to consider the bulk of the fuel, its cost, 

it- handling, and the readiness with which it may be fed 

into the engine. It is the total effect of all these factors 

the balance-sheet that is the important thing from 

the commercial point of view. 

Prom whal ha^ all the energy latent in naturally 

ing fuel i derived ? Gebrge Stephenson, when 

he l d what drove his locomotive, replied that it 

\\a> "bottlcd-up sunshine," and hi was not far wrong. 

will a^k how the bottling p r o ccsa was carried 

I that i- another rtory, which must be postponed 

to a later chap 






CHAPTER XIV 
FLAME: WHAT IS IT? 

THE reader will by this time have become fairly 
familiar with the conception of combustion, and 
he may be under the impression that, knowing 
what combustion is, he has nothing more to learn about 
flame. This would be a somewhat rash conclusion, for, 
to begin with, the one thing does not always accompany 
the other ; there are cases of undoubted combustion in 
which there is no real flame. A little piece of charcoal, 
for example, burning in air or oxygen gives out no flame ; 
it only glows. 

As a matter of fact, it is only when the burning sub- 
stance is in the form of gas or vapour that we get flame 
produced. It is true that many liquid and solid substances 
give a flame when they burn, but the production of the 
flame is preceded by their conversion into vapour. By 
holding a match to the wick of a candle we first melt 
and then vapourise the wax which is in the wick ; the 
vapour catches fire and the candle is lit. Once this has 
been done, the heat of the flame keeps the wax round 
the base of the wick melted, the melted wax is sucked 
up the wick by capillary action, and at the top it is 
vapourised and ignited. 

Flame, then, is something different from combustion, 
and may be defined as gaseous matter which has been 
raised to such a high temperature that it is obvious to 

154 



FLAME: WHAT IS IT? 




the eve. Solids begin to emit light when they are heated 
to about 900° Fahrenheit, but vapours must be raised 
to a very much higher temperature before they become 
visible When a combustible vapour re- 
acts chemically with the oxygen in the 
air, which is the supporter of com- 
bustion, the heat produced is intense 
enough to raise the vapour to the 
point of incandescence — a flame i> pro- 
duced. 

We have spoken here of a com- 
bustible substance and a supporter of 
combustion as being necessary for the 
production of flame, but it is well to 
rememlx'r that these term- are purely 
relative. If we could picture this 
world and its inhabitants as quite dif- 

t from what they are, and could 
imagine that the atmosphere round the 
globe wa> one of hydrogen instead of $& — 
air, then the gas companies would have 

ipply us with oxygen for lighting 
and heating purposes. I j 1 such a world 
jen would be regarded as the com- 
bustible substance, and hydrogen as the 

rti r of comb u stion. 
It i-, in fact, easy to -how thai air 
burns in ooal gas quite as readily as 

gas bums in ai)-. In the Accompanying Pig, I the 
apparatus ; for this experiment is shown, a 

lamp gla>s j. fitted ai the bottom with a cork, through 

which pa— two tub'-. The one which ends jus! above 

the cork is connected with tin- gas supply, the longer 




Fig. I.— A skptch of 

an experiment show- 
ing that air can be 
burned in an atmos- 
phere of coal pa?. 



FLAME: WHAT IS IT? 

one serves as an air passage. The top of the lamp glass 

is covered with an asbestos disc, in the middle of which 

there is a hole. When the gas is turned on, the air in 

the lamp glass is driven out, and the latter then contains 

an atmosphere of coal gas, the excess of which escapes 

through the disc at the top. This escaping gas may be 

lighted, and gives the ordinary flame of coal gas burning 

in air. If, now, the long tube which passes 

through the cork at the bottom is pushed up 

until it reaches the burning jet at the top, 

something at the end of this tube is seen to 

catch fire, and to remain alight, giving a visible 

flame even when the tube is drawn down 

again. The explanation of this interesting 

phenomenon is that air is being drawn up the 

long tube and is burning in the atmosphere 

of coal gas which surrounds the end of the 
Fig. 5.— The J? . . . 

flame of tube. Ihis apparatus, then, in which we can 

burning see both coal gas burning in air, and air 
hydrogen. b urn j n g j n coa j g as? shows that the terms 
" combustible," and " supporter of combustion " are inter- 
changeable. There is no real distinction ; the chemical 
process which goes on is the same in both the flames 
observed. 

When we come to look more closely at a flame we find 
that it has a structure. It may seem odd to speak of a 
mobile, elusive thing like a flame as having a structure, 
and certainly with a mixture such as coal gas being con- 
sumed at some ingenious modern burner, it is not easy to 
detect this structure. But if we take a simple gas such 
as hydrogen burning at the end of a plain round tube, we 
find the character of the flame to be exceedingly simple. 
The actual flame, as will be seen from the accompanying 

156 




FLAME: WHAT IS It? 





sketch, is confined to a certain lone or sheath in which the 
combustion ifl going on, and this oone-like sheath is hollow. 
That the cone of Manic is hollow may he very easily and 
prettily shown by suspending the head erf a match just 
above the end of' the tube before 
lighting the gas. In spite of the 
burning gas the matchin the inside 
remains unaffected (see Pig, (i, a). 
But we can go a step further and 
show that this hollow part of the 

flame contains unburn! gas by 

'fully putting one end of a 
narrow tube in the centre of the 
cone and applying a light to the 
other end some distance away. 
We get a flame there (see Fig. 6, b) 
simply because with the tube we 
have succeeded in leading off some 

of the unburnt gac from the centre 
of the cone. 

A candle flame and a coal-gas 
flame differ from a hydrogen flame 

only in that their structure is a 

little more complicated ; their 
general characteristics are similar. 
In these two cases the dark hollow cone in which is the 

unburnt vapour IS surrounded by a white, luminous /one, 
and this again by an outer envelope- of flame which is nun- 

luminou- and very difficult to see This outermost sheath 
bviously the one far which there is an unlimited supply 

©fo tiling which has escaped eombu>tion in 

the lumino ii there completely burned to carbon 

dioxide and 



<;. C. The bollOW nature 

of a tiame may be shown 
in various ways. A mat oh. 
head suspended in the 
centre is nut ignited by 
the flame, and with a piece 
of gla^s tube the unburnt 
gaa from the centre of the 
tiaine can be led off and 
Ml alight at the end of 
the tube. 



FLAME: WHAT IS IT? 

The luminosity of flame varies very remarkably with 
the nature of the combustible substance and with the 
conditions under which the combustion takes place. A 
hydrogen flame is quite non-luminous, carbon monoxide 
burns with a pale blue flame, while a candle or coal gas 
gives a bright white illumination. One cause of lumin- 
osity has been already referred to in a previous chapter, 
namely, the presence of solids which are made incandescent 
by the heat of the flame. A coal-gas flame contains in its 
luminous zone a host of unburnt carbon particles which 
are raised to a very high temperature and so give out a 
strong light. By mixing the gas with air before it comes 
to the nozzle of the burner these carbon particles are 
completely oxidised, and the flame becomes non-luminous. 
Such a non-luminous flame may, however, again be rendered 
useful for purposes of illumination by the artificial intro- 
duction of incombustible solids which are made incandes- 
cent by the heat of the flame. This is what is done in 
the ordinary incandescent gas burners and in the lime 
light. 

There are other causes which determine the luminosity 
of a flame besides the presence of solid particles. There 
are some flames known which are characterised by very 
high illuminating power, and in which at the same time 
there cannot possibly be any solid particles present. For 
example, phosphorus burning in oxygen produces a dazzling 
light ; but the oxide of phosphorus which results from the 
combustion is converted into a vapour at a red heat, and 
it is therefore impossible that it could exist in the solid 
state in the phosphorus flame, the temperature of which 
is far above the melting-point of platinum. 

The well-known English chemist Frankland, who made 
many experiments on the nature of flame and the cause of 

158 



FLAME: WHAT IS IT? 

its luminosity, once took the trouble to carry candles up 

to the top of Mont Blanc, and was much struck by the 
Comparatively small amount of light which they emitted 
when burning there. He traced this decrease of luminosity 
to the small atmospheric pressure prevailing at such a 
high level, and was able to show subsequently in his 
laboratory that the illuminating power of a candle is 

much reduced when it is burning in a partially exhausted 
A. 

Since diminution of pressure reduces the luminosity of 
a flame, it might fairly be expected that increase of 
lire would have the opposite effect : and so it turns 
out. A spirit-lamp, which, as the reader knows, give 
tically no light when burning in air under ordinary 
condition-, gives a highly luminous flame when placed 
under a pressure of four atmospheres ; and Frankland 
estimated that under a pressure of five or six atmospheres 
its luminosity would be equal to thai of sperm oil burn- 
ing under ordinary atmospheric pressure. 

The influence of pressure on the luminosity of a Hame 
is mosl strikingly illustrated by the effect of oompre - 
Mon on burning hydrogen. This gas burns under ordin 
conditions with a pair flame, absolutely Useless for illumi- 
nating purposes, and it might be supposed that the 

want of luminosity i^ due to the absence of any solid 

imbustion : water, the compound which 

lit! from the union of hydrogen and Oxygen, i , of 

course, a vapour at the temperature of the flame. But 

if hydrogen i- burned in oxygen at ten atmospfa 
ore, the Lighl emitted by the flame is sufficient to 

enable the d a new paper two .v. 

Plainly, ii. . tin- p re s en ce of solid particles is 

not the only thing on which the luminuit\ of flame 



FLAME: WHAT IS IT? 

depends ; the pressure under which the flame is burning 
has a decided influence. 

We must recognise also another factor which has a 
bearing on the luminosity of a flame, and that is its 
temperature ; the hotter a particular flame is, the higher 
is its luminosity as a general rule. One way of raising 
the temperature of a flame is to feed it with oxygen 
instead of air, and the result of doing this is some- 
times surprising. The temperature, for instance, of a 
hydrogen flame in air is about 3600° Fahrenheit, while 
the same flame in an atmosphere of oxygen is some 
1400° hotter. It is true that in the case of hydrogen 
no increase in luminosity results from this very remark- 
able rise of temperature, but the behaviour of hydrogen 
is exceptional. If a candle burning in air is transferred 
to a jar of oxygen, the flame shrinks in size but becomes 
distinctly more luminous, owing to the higher tempera- 
ture. 

We may get a hotter flame also by heating the air 
and the^as which are supplied to the burner, and such 
a rise in the temperature of the flame leads to increased 
luminosity. This was the principle applied in the so- 
called " regenerative " burners, in which the usual glass 
chimney was surrounded by a wider one closed at the 
bottom ; the air, therefore, which fed the flame had to 
pass down between the chimneys, and was very con- 
siderably heated by contact with the inner one. Such 
devices, however, for securing increased luminosity have 
disappeared before the incandescent burner. 

Not only may a flame be made hotter in various 
ways ; it is possible also to lower its temperature. Ad- 
mixture of an indifferent gas — that is, one which takes 
no part in the combustion — produces a marked cooling 

160 



FLAME: WHAT IS IT? 

effect, and a similar result is obtained by introducing 
into the flame some body which is a good conductor 

of heat. Indeed the temperature may he m) nineh 
lowered by this latter device that the flame IS extin- 
guished. If. for example, a coil of copper wire IS care- 
fully placed over the wick of B burning taper, the flame 
out immediately. 
In order to understand the possibility of this pheno- 
menon, we DQUSl remember that every inflammable vapour 
has a certain ignition temperature. That is to 
for each vapour there is a point to which it musl be 

heated in presence of air before it will catch lire and 
give a flame. Once it has been ignited, the heat given 
out by the flame as the result of the chemical action 
raises the incominj above the ignition tempera- 

ture, and ao the combustion continues. 

Different substances have wry different ignition tem- 
peratun The vapour of carbon disulphide can be 
ignited by contact with a glass rod which has been 
heated only to Fahrenheit, a little higher than 

the temperature of boiling water, .V current of hydro 
issuing from s tube is ignited by sparks from a flint 
and >teel, whereas marsh gas is quite indifferenl to 
BOch treatment. 

Ti. bility of cooling an inflamed vapour below 

it- ignition temperature may be demonstrated in a very 
simp i .11 in Pig, 7. </. a piece of copper 

wire game is j down on a Hone of burning coal 

gas (which. llready Been, contain- a large 

proportion of marsh gas), no combustion take place 

abo\e the although it I to how thai 

there i- inflfimmaMf rapoUT their by oiinuino; up a 

lighted hold the game an inch 

L61 i. 



FLAME: WHAT IS IT? 



or two above a nozzle from which coal gas is issuing, 
we may light the gas above the gauze without the flame 
passing through to the lower side (see Fig. 7, b). The 






Fig. 7. — Showing the difficulty which a flame has in passing from 
one side to the other of a wire gauze. 

reason of this curious result is that copper is an excellent 
conductor of heat, and the interposition of the gauze 
has such a cooling effect that the inflammable vapour 
on the other side from the flame is kept below its 
ignition temperature. 

162 



FLAME: WHAT TS TT ? 

As already stated, the ignition temperature of hydrogen 
is lower than that of' marsh gas, and it' we attempted 
to obtain with hydrogen the results jus! described, wt 
should not succeed. In all cases the hydrogen flame 

would strike through the gauze. 

The remarkable power of metal gauze to limit the 

extension of a marsh gas flame was utilised long ago 

in the well-known miner's safety lamp devised by Sir 
Humphry Davy. Coal measures are frequently highly 
charged with marsh gas, and large quantities of this 
find their way into coal mines. Since this " tire- 
damp, "" as it is called, is inflammable, and forms a very 
explosiw mixture with air, its presence in these mine* 
i- a source of great danger, and has repeatedly led to 
serious disasters. 

The risk of Using naked flames in such " ga~ v 
mines had ta l)e got oyer somehow, and Davy was able 
to show that if the oil flame in the miner's lamp was 
s ur ro un ded by wire gauze the danger of explosions was 
very much reduced. An explosiye mixture of fire-damp 
and air will not as a rule be fired by such a lamp, but 
will indicate it- presence by binning inside, and so 
wain the miner of danger. The action of the gauze 
in conducting away tin- heat prevents the explosive 
mixture outside reaching it- ignition temperature. 

The old form of Davy lamp has been found defec- 
in Mune respects, and has been continuously im- 

I -d ; thus the wire gauze cut off a givat deal of 

the light, -o the lower pari vras replaced by 
cylinder. Then it was found thai s strong draught 
hi blow the flame ag ind even through the 

gauze, irith the mull thai plosive mixture outside 

Id be ignited. The newesl form of tlit- safety lamp 



FLAME: WHAT IS IT? 

is therefore fitted, not only with a glass cylinder at 
the bottom to let the light out, but with an iron 
cylinder above to shield the lamp from draughts. 

When the Davy lamp is brought into an atmosphere 
in which fire-damp is present, a so-called " cap " of pale 
blue flame is seen surmounting the ordinary luminous 




abed 

Fig. 8. — A flame of burning hydrogen is shown at (a). When this 
flame is brought into an atmosphere charged with fire-damp or 
marsh gas it is surmounted by a "cap," the length of which 
indicates the amount of dangerous vapour present. The caps 
shown at (6), (c), and (d) represent what is seen when the atmos- 
phere surrounding the flame contains one-half, two, and three 
per cent, of marsh gas. 

flame in the lamp. The length of this " cap " increases 
as the percentage of fire-damp in the surrounding atmos- 
phere rises. Hence it will be seen that to the experienced 
eye the appearance of the Davy lamp flame serves as a 

164 



FLAME: WHAT IS IT? 

mean> of estimating the amount of fire-damp. It is only 

a rough estimate, however, which can be made in this w ay. 
In recent years a much more accurate method of 
estimating the amount of fire-damp in mines or of 
petroleum in air has conic into vogue. The apparatus 
u>ed is really a safety lamp in which hydrogen is burned 
in-tead of oil. In an atmosphere containing fire-damp 

:>>*" appear on the hydrogen flame just as in the ordi- 

ty lamp, but owing to the fact that the hydrogen 

flame is much less luminous than the oil flame, the "caps" 

are more easily seen and measured. The accompanying 

8 shows the nature of these "flame caps," and the 

in which their length varies with the amount of fire- 
damp in the atmosphere. 

The gradual development of the Davy lamp is an 
interesting example of the way in which scientific work 

been directed to the detection of danger and the 

ation of life. It would indeed be difficult to 

estimate the saving of human lives which has resulted 

from Davys discovery of the valuable properties of metal 

wire gauze in relation to a marsh gas flame 



165 



CHAPTER XV 
EXPLOSIONS AND EXPLOSIVES 

THE reader may at some time have seen or handled 
those curious little things known as " Prince 
Rupert's drops." These are obtained by allowing 
drops of molten glass to fall into cold water, where they 
solidify in a tadpole-like shape. If the tip of the tail of 
one of these drops is nipped off with the fingers, the whole 
thing breaks up into dust with a loud explosion. The 
reason is that the glass which forms the solid drop is in a 
state of intense strain owing to the very sudden cooling 
which it has undergone ; the outside and the inside of the 
drop have cooled at different rates, the particles of the 
glass are in a state of unstable equilibrium, and the 
slightest jar upsets the whole structure. 

There are many chemical compounds which exhibit 
considerable analogy with Prince Rupert's drops. The 
molecules of these compounds have been formed by the 
combination of a number of atoms, but the equilibrium 
between the latter is an unstable one, liable to be disturbed 
by the most trivial exciting cause. 

An example of this curious behaviour is furnished by 
nitrogen iodide. This extraordinary substance is prepared 
by the action of iodine on ammonia, and although 
generally quite stable in the moist state, it has been 
known to explode even under water. As usually obtained, 
it is a chocolate-brown powder which explodes violently 

166 



> 








-r •*- " *^ 



Wn\i Modi Do 

voodcn boom >ias been blown up ami ( 
the immense body of water raised by the force of the explosion. 



EXPLOSIONS AND EXPLOSIVES 

on the slighte-t provocation; if it is dry, the falling ot 

dust particles, the tread of a fly, or the merest touch with 
a feather, will be sufficient to make it go off with a bang. 
The molecule- fly to piece-, and a quantity of nitrogen gas 
and iodine vapour is generated, occupying much more 
space than the original -olid substance. 

ensitivi material is obviously most dangerous 
to handle, but there are other compounds which exhibit 
the same character of unstable equilibrium, and which 
yet can be manipulated safely if due care is taken. As 
we -hall see later, these readily exploded substance- fulfil 
a useful function. One which is extensively employed, 
and which on that account deserves special notice, i* 
mercury fulminate. 

Thi- is prepared from mercury, nitric acid, and alcohol, 
and when pure i- a shiny white, crystalline substance con- 
taining the elements mercury, carbon, oxygen, and nitro- 
; -mot be kepi in a glass-stoppered bottle, for 
the men ll th< stopper and the neck would 

l it to explode. When struck with a hammer 
mercury fulminate goes off with a very sharp report, 
evolving a large quantity <>f gas— nitrogen, carbon 
monoxide, and mercury vapour. If is, of course, one of 

the essential elr tics of an explosive thai a -mall 

quantity of th< stance should yield suddenly a very 

olutae of ga& In th- of fulminate it is 

'1 thai the gas produced by its explosion would 
\i the ordinary temperature 1800 to 1 too til 

the bulk of thfl ml L£ Rut the actual volume 

of I much larger than that, for 

in ti the fihiiiii I imouiif of 1 

i^ lil in vir( rhicfa tfa ! to 

a hi i much largi i 

L67 



EXPLOSIONS AND EXPLOSIVES 

The fact that mercury fulminate when it decomposes 
produces heat is worthy of notice, for it is a phenomenon 
rather different from what might be expected. We have 
seen that as a rule the chemical combination of elements 
is accompanied by the evolution of heat ; the process is 
said to be "exothermic." This being so, we may con- 
fidently anticipate that the reverse process, the decom- 
position of the compound into its elements, would use 
up heat, and therefore, if it took place spontaneously, 
it would be accompanied by an absorption of heat. This 
is quite a sound conclusion, but it is obvious that mercury 
fulminate, the decomposition of which leads to the produc- 
tion of much heat, must belong to a different category. 

The secret of the explanation is that, although the 
formation of most compounds is accompanied by the 
evolution of heat, there are some — " endothermic " com- 
pounds, as they are called — the formation of which is 
accompanied by absorption of heat. In this case the 
reverse process, in which the compound decomposes into 
its constituent elements, will be accompanied by the 
evolution of heat. So it is with mercury fulminate, 
which is an endothermic compound, and, like others of 
this class, is peculiarly liable to sudden decomposition. 

As a matter of fact, the explosion of mercury fulminate 
is accompanied by the evolution of more heat than is 
involved merely in the splitting of it into the constituents, 
for two of the elements liberated in this primary decom- 
position, namely, the carbon and the oxygen, immediately 
unite to form carbon monoxide, and as this combination 
is an exothermic process, the heat produced by the 
explosion is much augmented. 

The explosive disruption of the molecules of nitrogen 
iodide and mercury fulminate is due to the want of 

168 



EXPLOSIONS AND EXPLOSIVES 

cohesion hetwem the constituent atoms; it is the old 
story of a house divided against itself Bui mosl of the 
explo^on^ whidl eonie about, intentionally or uninten- 
tionally, depend on an altogether different principle; 
they imply combustions which take place with 

ipidity, and which result in the production 
of quantities of pi\ Tn such explosions the element 
gen play- an essentia] part. 
In any inflammable gas or \apour will 

explosive mixture with air. The reader must 
fully distinguish between "inflammable* and "ex- 
plosive"; it is not correct to speak of coal gas ib 

plosive"; it is certainly inflammable, and when 
ignit ' le nozzle, burn- quietly as long as the 

supply lasts. Combustion take- place only when air 
meet. A mixture of coal gpa with air is, how- 
ever, a very different thing; it is inflammable at every 

it — explosive, in fad : combustion once started is 
rapidly pro] I through the bulk of the mixture. 

Irogen similarly forms an explosive mixture with air, 
and illustrations of this fact are not infrequent in a 

mica] Laboratory. For it often happens that a 
beginner, preparing hydrogen in a flask by the action of 
an acid on a metal, applies a light to the issuing 
before all the air ha- been expelled. The result of this 
will probably be that part of the Ma-k will adhere to the 

1 will be converted info fine dust 
That coal gas beo when mixed with air 

frequently reminded, as from time to time 
read of ho ha- look for ;< leak of gas 

with a light adle, and baa thereby brought 

on himself and his surroundings. When we 

he atmosphere there i> a 
169 



EXPLOSIONS AND EXPLOSIVES 

mixture, possibly explosive, of coal gas and air, and if 
we were to carry a naked flame in search of the leak, 
we should be as foolish as the miner who goes into a 
" gassy " mine with a lighted candle. To produce an 
explosive mixture of air and coal gas about 6 per cent, 
of the latter is sufficient, so that one cannot be too care- 
ful. The only safe course is to begin by ventilating the 
house thoroughly, so that the proportion of gas may be 
reduced below the explosive limit. 

In explosions of this kind, where both parties to the 
combustion are gaseous, the amount of gas produced by 
the explosion is relatively less than in those cases where 
the original unexploded substance is a solid. The increase 
in volume is in fact due solely to the high temperature 
caused by the heat of the combustion. If coal gas and 
air, in the proportion of 1 to 5 by volume, are exploded in 
a very strong closed vessel so that no expansion is possible, 
a pressure of 7 to 8 atmospheres is developed, and the maxi- 
mum temperature reached is nearly 3500° Fahrenheit. 

Explosions in which the oxygen necessary for the 
combustion is supplied in the form of air are actually 
employed as sources of energy in gas- and motor-engines. 
The pressure developed when a mixture of gas or 
petroleum with air is exploded is used to move a piston, 
and the longitudinal motion of the piston is converted 
into circular motion as in a steam-engine. It has been 
said that fire is a good servant but a I i :..c Ler, ar 
the remark is true in reference to explosive as well as to 
ordinary combustion. 

If instead of using a mixture of two gases w '.ake a 
solid combustible material, and mix it intimately with 
some other substance which not only contains a large 
proportion of oxygen but is fairly ready to part with 

170 




c 2 

s j 



_ u 

z 5. 



< a 

— 



EXPLOSIONS AND EXPLOSIVES 

some of it, then, on the supposition that the combustible 
material yields gaseous products when it is burned, the 
mixture of the two solids will be a compact explosive. 
It will be compact because its bulk will be small in com- 
parison with the volume of the gases produced by its 
i xplosion. 

( ommon gunpowder is an explosive of this kind. It 
i intimate mechanical mixture of the three substances — 
potassium nitrate (nitre or saltpetre), charcoal, and sulphur. 
The first and second of these are the essential constituents 
gunpowder; the sulphur is present in a smaller pro- 
ion, and is added for a special purpose which will be 
explained later. 

The charcoal and the sulphur, as the reader will under- 
stand, are the combustible constituents, and the saltpetre, 
which forms about three-quarters of the gunpowder, is a 
pound which contains a high proportion of oxygen, 
and which, moreover, is easily induced to pari with some 
of it : this being SO, saltpetre may be regarded as a coni- 
form of oxygen. Anyhow, it is easy to show that 
charcoal and saltpetre, while quite ready to lie down 
•fully together at the ordinary temperature, act 
ntly on each other when heated ; any one can con- 
vince himself of this by throwing a pinch of saltpetre on 

It is v< trad the potassium nitrate from 

gunpowder. and it i> worth the reader's while to try this, 

the process illustrates very forcibly what was said 

in an earlier pari of this volume about the separation of 

the constituents of a mechanical mixture, and shows, too, 

simple operations of which the chemist make- 

dail T der is boiled vritfa "h)c\\ and 

then filfa red : B paper I one made of 

171 



EXPLOSIONS AND EXPLOSIVES 

blotting-paper, the sulphur and the charcoal, being in- 
soluble in water, are held back, and a colourless solution 
runs through the blotting-paper into a vessel placed to 
receive it. This solution, when allowed to cool or when 
evaporated a little, will deposit white crystals of saltpetre. 

What takes place when gunpowder is fired is essentially 
a combustion of the charcoal, as a result of which large 
quantities of gas — carbon dioxide, carbon monoxide, and 
nitrogen — are suddenly evolved. The presence of the 
sulphur makes it more easy to fire the gunpowder, a 
lower temperature being sufficient to set it off*; the 
function of the sulphur is therefore similar to that which 
it used to fulfil when employed in coating matches. In 
addition, however, the presence of the sulphur contributes 
to the rapidity with which the explosion is propagated, 
and its oxidation by the saltpetre adds materially to the 
heat evolved in the reaction. 

The advantage of having the explosive material in a 
compact solid form can be seen from the fact that when 
gunpowder is fired in a closed space the pressure developed 
is about 2000 atmospheres, quite a different magnitude 
from the pressures obtained in the explosion of coal gas 
and air. 

Gunpowder is the oldest explosive known, but it is 
largely displaced nowadays by so-called " high explosives," 
which, in addition to several other points of distinction, 
are practically smokeless. Any one can understand the 
long-cherished desire of the military and naval specialist 
to find some substitute for gunpowder, which when fired 
envelops the operator of a gun in a dense cloud of smoke. 
In the chemical action which accompanies the explosion 
the potassium from the saltpetre forms other salts, 
potassium carbonate and potassium sulphate. These 

172 



EXPLOSIONS AND EXPLOSIVES 

substances are dissipated by the force of the explosion 
in a state o( fine division) and form the smoke. Prom 
such Baits the modern high explosives are free, and they 
arc consequently smokeless, or very nearly 90. The 
applications of gunpowder are therefore more restricted 
than they once were. For firearms, large and small, i1 
been replaced by smokeless powders, but it is till 
largely employed for blasting purposes. It enter si 
into the composition of fireworks, in which, however, 
issium chlorate frequently acts as the oxygen-supplying 
constituent instead of saltpetre. 

In the manufacture of modern high explosives a new 
and interesting principle has been introduced. Gun- 

ler. as we h n, is an intimate mixture of three 

-olid-, two of which are readily combustible, while the 
third supplies the oxygen necessary for combustion. Jn 
gunpowder may be a good explosive it is 
manifestly essential thai the mixing of the constituents 
ery thorough ; provision must be made, as it 
wen h combustible molecule finding near at hand 

tlecule out of which it can get the ne 
thai when the powder is fired no time may be 
[plosion may be as rapid as possible. \ 

amattt at pain- are taken in the manufacture 

unpowder to the mosl thorough miring of the 

Now in th xplosivec the oxygen is intro- 

duce ompound which lie alo 

fflStitaent, bu1 actually in the 

molecule In other words, chemical oompoum used 

id of in- 1 I mixtures such a gun- 

Thi- d ilmosi 

of the with the oxygen, and the 



EXPLOSIONS AND EXPLOSIVES 

natural result is that these modern explosives go off with 
much greater rapidity than gunpowder. It may seem 
strange to the reader that we can prevail on atoms of 
carbon, hydrogen, nitrogen, and oxygen to form for a 
time a peaceable combination which is ultimately to be 
rent asunder with such violence, and it must be confessed 
that the arrangement into which they are coaxed is some- 
what of the nature of an unstable equilibrium, easily 
upset by any irritating cause. In this respect these high 
explosives have some resemblance to nitrogen iodide and 
mercury fulminate, but the process of explosion in the 
former cases is a real combustion, which the explosion of 
nitrogen iodide and fulminate is not. 

Gun-cotton, nitro-glycerine, and picric acid, which 
either alone or in combination with other substances 
form the majority of the high explosives, are obtained 
by the action of nitric acid on cellulose, glycerine, and 
carbolic acid respectively. Nitric acid is a substance 
which contains a large proportion of oxygen, and its 
action on these materials is such that new substances are 
formed provided with a good deal of the oxygen which 
was previously in the nitric acid. The various explosives 
just mentioned are alike in containing a particular group- 
ing of nitrogen and oxygen atoms known to chemists as 
the " nitro " group, and gun-cotton and the rest of them 
are therefore frequently referred to as the "nitro- 
explosives." 

It is indeed very remarkable that a harmless thing 
like ordinary cotton when treated with nitric acid should 
undergo such a fundamental change, and be converted 
into a powerful explosive. Great care has to be taken 
in the process of manufacture, and only the best white 
cotton waste, perfectly free from grease and dirt, can 

174 




^ u_ 












,,¥' 

?*.... 






EXPLOSIONS AND EXPLOSIVES 

be employed. During the time the cotton is in contact 
with the nitric acid the temperature must be kept down, 
and subsequently every trace of acid must be washed 
away with water. It was owing to wanl of attention 

to this lasl >imple precaution thai many of the explosions 

which attended the early manufacture of gun-cotton were 
due. Any trace of acid left in the finished article acts 
like an irritant, and leads sooner or later to the decom- 
ition of the explosive 

Gun-COtton is a most curious substance. It takes fire 
much more easily than gunpowder, and the rate at which 
it bums altogether depends on the way in which it has 
been ignited, and the conditions to which it is subject. 
A piece of loose gun-cotton may actually be burned on 
the hand without scorching the skin, merely by touching 
it with a hot glass rod; it can be fired on the top of a 
hea|) of gunpowder without igniting the latter. Under 
such condition- the combustion of the gun-cotton is 
rapid, but not explosi\e. When, however, it is filed in a 
fined space, and the flame from the portion first 
ignited is driven into the remaining mass, the tem- 
perature is forced up and the combustion becomes an 
explosion. 

It was therefore very naturally thought for a long 
e that in order to utilise the explosive force of gun- 
cotton it must be enclosed in some strong casing. Some 
foity yean ago, however, the veiy interesting discover] 
was that this was unnecessary, and that gun- 

ton which r ly c omp ressed, not confined in an 

could \h- exploded bj a d or, retch 

as mercury fulminate It i indeed a curioui fact that if 
a little of thifl ltttri rabstam cploded in the im 

j hbourhood I unoonfin ipn ed 



EXPLOSIONS AND EXPLOSIVES 

gun-cotton, the gun-cotton explodes with extraordinary 
violence. 

It is well known that if a violin is made to emit a 
particular note, the string of a second instrument in the 
immediate neighbourhood, if tuned to that note, will take 
it up and vibrate spontaneously. Some chemists have 
thought that something analogous to this takes place 
when mercury fulminate is exploded in contact with gun- 
cotton ; the vibrations set up by the detonator are sup- 
posed to excite similar vibrations in the gun-cotton, so 
much so that the latter undergoes what might be called 
a sympathetic decomposition. 

Whether this is the correct explanation or not, there 
is no doubt that gun-cotton fired by a detonator gives a 
much greater effect than the same material fired in the 
ordinary way. This increased effectiveness is due to the 
greater rapidity of the explosion induced by the detonator. 
Thus if a train of ordinary gun-cotton is touched with 
a hot rod the resulting combustion advances only a few 
feet in several seconds, whereas if a train of compressed 
gun-cotton is detonated by mercury fulminate it is 
estimated that the explosion is propagated along the train 
at the rate of 200 miles a minute. 

Perhaps still more curious and valuable was the dis- 
covery that wet gun-cotton, which is not explosive under 
ordinary conditions, could be detonated as easily as the 
dry material. A red-hot iron may be put into a mass of 
wet gun-cotton without setting it on fire ; and a Govern- 
ment Committee, in order to demonstrate incontestably 
the possibility of safely storing this explosive in the moist 
condition, once instituted experiments in which an iron 
case, containing a ton of wet gun-cotton was put in a 
magazine and surrounded with shavings and other in- 

176 



EXPLOSIONS AND EXPLOSIVES 

flammable material. This was then ignited, and when the 
combustion was over the case of wet gun-cotton was re- 
red, none the worse tor its baptism of fire. 

Wet gun-cotton, however, can be at once exploded by 
detonation, provided only that a little of the dry material 
is in contact with the detonator. The old saying, there- 
fore, u Keep your powder dry," is applicable only in a 
rery limited sense to gun-cotton. It is, as a matter of 
fact, always stored in the wet state, containing about 
twenty per cent, of water: and it may be used in this 
condition in torpedoes and submarine mines. 

A more dangerous explosive than gun-cotton is nitro- 
glycerine, a liquid obtained by the action of nitric acid 
on glycerine. The most extraordinary precautions have 
to be taken in the handling of this material, and it is 
only by a strict observance of these that a repetition 
of the disasters which marked the early years of nitro- 
glycerine manufacture is avoided. So serious were the 
accidents which occurred with nitro-glycerine some forty 
years ago that several governments went the length of 
altogether prohibiting the use of the explosive. Chemists 
soon discovered, however, the necessary precautions that 
have to be taken in the manufacture and handling of 
nitro-glycerine, and at the present day large quantities 

of thi- explosive arc- prepared 

In a nitro-glycerine factory the sheds in which the 
\ari< rations are carried on are well separated from 

. and surrounded by bank- of earth or sand. 
In order to avoid any ri>k of a -park being produced 
and off the nitro-glycerine, all workers have to 

1 clothing. Hoots with iron nail- are abso- 
lutely prohibited, and in their place -hoc. of rubber, 

felt, or town leather an employed Girl operative! 

1 : 1 m 



EXPLOSIONS AND EXPLOSIVES 

are forbidden hairpins, and no one is allowed to carry 
any article made of iron, such as knives or keys, for 
these by friction might give rise to a spark. 

Such precautions being necessary, the reader will 
understand that the handling and transport of nitro- 
glycerine by the uninitiated person is fraught with 
great danger. Hence before it leaves the factory it is 
converted into various forms which involve less risk. 
The commonest of the explosive materials thus based 
on nitro-glycerine is dynamite. Certain substances have 
the power of soaking up or absorbing nitro-glycerine, 
and one of these which has been found very satisfactory 
is an infusorial earth known as kieselguhr, which takes 
in as much as three times its weight of nitro-glycerine. 
The resulting product is dynamite, a material which is 
less violent than the parent substance, and more easily 
and safely handled. Indeed, it was not until the little 
device of employing absorbent kieselguhr was adopted 
that the manufacture of nitro-glycerine assumed practical 
and commercial importance. This may be gauged from 
the fact that in 1870 the world's output of dynamite 
was only 11 tons, while twenty years later it had risen 
to 12,000 tons. 

Dynamite, like gun-cotton, burns without danger when 
loose and in small quantity, but when fired by a detona- 
ting fuse of mercury fulminate it explodes with extreme 
violence and rapidity. Indeed, it is estimated that the 
time occupied in the explosion of a dynamite cartridge 
is only -ztgtsts of a second. One consequence of this is 
that when dynamite is used for blasting rock, the usual 
bore-holes may frequently be dispensed with, and the 
explosive may be laid on the top of the rock, covered 
merely with a little earth or clay. 

178 







< 
- 



D 
O 

- 
- 



Q S 



EXPLOSIONS AND EXPLOSIVES 

The greater sensitiveness of dynamite as compared 
with gun-cotton is well illustrated by their different 

iviour when fired at with a rifle. It* a wooden box 
tilled with dry compressed gun-cotton ifl exposed to this 
treatment, the contents of the box are generally inflamed 
but never exploded. Dynamite, on the contrary, and 

]• explosives derived from nitro-glyeerine, cannot 
contain themselves when treated in such a fashion, and 
go ofl' with great \ iolence. 



179 



CHAPTER XVI 

BELOW ZERO 

IT is an old tale that Fahrenheit took as the zero of 
his thermometer the lowest temperature which was 
observed by him at Dantzic during the winter of 
1709, and one of his contemporaries remarks that Nature 
never produced a cold beyond zero. This is quite a 
mistaken view, for plenty of cases are on record in which 
considerably lower temperatures have been observed as 
the direct result of natural cold. By artificial methods 
it is possible to realise a much greater degree of cold, 
and within the last ten years temperatures of about 
— 400° Fahrenheit have been reached. As the mercury 
in our thermometers freezes at about —40° Fahrenheit, 
the reader will see that a lowering of the temperature 
to — 400° brings us to altogether new conditions. 

The way in which chemists and physicists have gradu- 
ally pushed forward into the region of low temperatures 
is very remarkable, and their discoveries are not only 
of fascinating interest to the student of Nature, but 
have in some cases proved of practical and commercial 
value. The ambition to get " farthest north " has led 
to many thrilling adventures, but the Arctic exploration 
carried out recently in the laboratories of England and 
the Continent is not a whit less romantic. 

The first step in the direction of low temperatures 
is taken when we can start with substances at the 

180 



BELOW ZERO 

ordinary temperature, and either by utilising some 
inherent property of these substances, or by treating 
them in some special way, induce the temperature to 
tall, say, below the freezing-point of water. 

The mere bringing together of two substances may lead 
to either a rise or a fall of temperature. The reader may 
remember the reference made in a previous chapter to the 
fact that when sulphuric acid and water are mixed, so much 
heat is produced that the containing vessel becomes too 
hot to hold. The opposite effect is frequently observed 
when other substances are mixed with water. When 
saltpetre or sal ammoniac, for example, is stirred into 
water, the cooling effect is very noticeable, and by this 
simple method ([iiite a considerable fall of temperature 
tt puduced. A mixture of these two salts, added to 
an equal weight of water at 50° Fahrenheit, brings the 
temperature down to 10° Fahrenheit. 

More marked and more persistent cooling effects are 

obtained, if, instead of adding salts to water, we mix them 

with powdered ice or snow. Any one who procures 

mon -alt and snow, stirs them up well in the proper 

portions, and puts a thermometer in the mixture will 

the mercury fall below zero Fahrenheit. Such a 

/ing mixture may be used not only for getting a low 

temperature in scientific experiments, but also for the 

lly practical, if less exalted, object of making ices. 

Hie question may very naturally be put: "Why 

should the mere bringing together of sail and miow resull 

Kcfa a marked fall of tempera! ure ? ** The answer to 

this question is very closely connected frith what pras said 
in a previous chapter about the melting-point of alloys. 
ntion iras then directed to the fact that the melting- 
point of anv metal i^ lo by the p of another 

L81 



BELOW ZERO 

metal. To the case of ice and salt a similar rule applies. 
Every schoolboy knows that pure water freezes at 32° 
Fahrenheit (0° Centigrade), but it is a curious fact that 
water containing salt does not freeze until a lower tem- 
perature has been reached. That means that a mixture 
of snow and a little solid salt should, strictly speaking, be 
in the liquid condition at 32° Fahrenheit ; there cannot 
therefore be true equilibrium between snow and salt at 
this temperature. 

Now, in Nature, things are always trying to get into 
the most stable condition possible, in other words, to reach 
their true equilibrium. Water finds its own level, a hot 
and a cold object put side by side gradually and of their 
own accord assume the same temperature, while positive 
and negative electricity unite whenever they get the 
opportunity. Similarly snow and salt, when mixed 
together at 32° Fahrenheit, do their best to get into that 
condition which Nature has prescribed as the most stable 
one for them at that temperature ; the result is that the 
snow melts and the salt dissolves in the melted ice. 

Now both these processes use up heat ; as they take 
place spontaneously, this heat is taken from the surround- 
ings, and the temperature of the mixture and of the con- 
taining vessel falls. The reader will at once admit that 
heat is required to melt snow, and he will see that the 
addition of salt is an ingenious way of persuading the 
snow to melt, and so to abstract a definite amount of 
heat from its surroundings. For the same quantity of 
heat is always required to melt a pound of snow, whatever 
be the way in which we cause the melting to take place. 

So far as we have gone, then, methods of producing 
cold depend either on dissolving a solid in a liquid, or 
on making a solid melt by a little scientific stratagem. But 

182 



BELOW ZERO 

just in utilise the change of solid into liquid as a 

means of reaching lower temperatures, bo we can employ 
another change of state for the same purpose — the change, 

namely, in which a liquid passes into the condition of a 
vapour. We usually convert a liquid into a gas or 

vapour by heating it ; for the conversion of water al 

Slf Fahrenheit into steam at 212°, heat is as necessary 

as it i^ for the conversion of ice or snow at o2° Fahren- 
heit into water at the same temperature. Evaporation, 
then — that is, the process by which a liquid is changed 
into a vapour — only takes place when heat is supplied. 
If by any means we can cause evaporation to take place 
without the external application of heat, then the neces- 
HUry heat will be taken from the evaporating liquid 
Itself and its surroundings. Under these circumstances 
: oration produces cold. 

A very simple way of causing a volatile liquid to eva- 
porate rapidly without heating is to blow a strong current 
of air through it. That by this method a considerable 
r« duction of temperature may take place can be shown by 
y rimple experiment. A small pool of water is made 
on the to]) of a flat wooden Hock, and in this pool i 

a flask containing strong ammonia solution. A strong 

current of air is then blown through the liquid with the 
aid of a bellow > ; the ammonia evaporates rapidly, and 
_ the flask IS frozen hard to the block. 
With these two general ways of producing cold at 

their dispoSI . I iday and other cfaemistfl after him have 
i able to obtain in the liquid state many substances 

which exist ordinarily a- invisible Tin- point to 

which the ten] of s gai must be lowered before 

it begins to liquefy will, of , vary from one case to 

another. If we could imagine tin- te mp er a ture of our 

188 



BELOW ZERO 

globe as being normally about 250° Fahrenheit, then 
water would exist only in the form of vapour or steam, 
and in order to liquefy it we should have to bring the 
temperature below 212°, the boiling-point of water. At 
any temperature lower than 212° steam will condense 
under the ordinary pressure of the atmosphere. Now 
we must remember that every other liquid has its own 
boiling-point, and substances which we know as gases 
are simply liquids whose boiling-points are at a tempera- 
ture lower than that prevailing on the surface of the 
globe. 

Sulphur dioxide, for example, the colourless, choking 
gas which is produced when sulphur is burned, is very 
easily obtained as a liquid at temperatures not much 
below the freezing-point of water. The boiling-point 
of this liquid sulphur dioxide is 18° Fahrenheit under 
the ordinary pressure, so that when the gas is passed 
through a tube surrounded by a freezing mixture of ice 
and salt, it condenses to the liquid form just as steam 
would do if it were passed through a tube surrounded 
by cold water. It is, in fact, quite easy to obtain liquid 
sulphur dioxide, and it is now sold in syphons, just as 
if it were so much soda water. 

When we come to gases like ammonia and carbon 
dioxide, which are less easily condensed, it is found advis- 
able to use high pressure as an aid to liquefaction. The 
reader will understand the object of this if he remembers 
that the boiling-point of a liquid gradually rises with 
the pressure to which it is exposed. For example, water 
boils at 212° Fahrenheit under a pressure of one atmos- 
phere, but at 250° when the pressure is two atmospheres. 
Conversely, then, when a gas is kept under high pressure, 
less cooling is necessary to bring it below its boiling-point. 

184 



BELOW ZERO 

By the combined application of cooling and compres- 
sion both ammonia and carbon dioxide are readily obtained 
in the liquid form, and they are now commercial articles, 
sold in steel bottle^ or cylinders. With the aid of liquid 
ammonia and liquid carbon dioxide we are able to go 
a long step farther in realising low temperatures, for the 
cold produced by their rapid evaporation IS very intense. 
This js well shown by what happens when the tap of a 
liquid carbon dioxide bottle is opened. The liquid is 
farced out in a fine jet by the high pressure which pre- 
vails in the bottle, and the cold produced by the eva- 
poration of the outer portion of the jet is so great that 
the inner portions are solidified to a white, snow-like 
powder. If a coarse canvas bag is tied over the nozzle 
of the bottle while the liquid is escaping, a quantity of 
this curious solid carbon dioxide may be collected. 

"Carbonic acid snow," as we may call it, can be placed 

on the hand without danger, but if pressed into the skin 

I ious blister is produced, the effect being pretty much 

the same as that caused by a red-hot metal rod. A 

number of interesting experiments can be made with 

solid carbon dioxide; if, for example, some of it is placed 

on the top of a little mercury in a dish, and some 

-pirit or ether is added, the mercury is very 

quickly frozen to a hard mass. In fact the temperature 

in this way is as low as —112° Fahrenheit; and 

mixture of ether and carbonic acid snow is made 
to e ry rapidly by connection with a suction 

ip the temperature reached is considerably lower still 
The temperature of — 1 1 U Fahrenheit just mentioned 
lie l>oi]ing-point of liquid carbon dioxide under 
atmc re; this substance is a conspicuous 

of what may be called "cold boiling liquids/ 
185 



BELOW ZERO 

and the reader will see that boiling does not necessarily 
mean a high temperature. That liquid carbon dioxide, 
kept in an open vessel, is very cold can be simply shown 
by thrusting a piece of metal into it. There is a hissing 
and a bubbling exactly similar to what is observed when 
a red-hot poker is thrust into water ; so that, relatively 
to the piece of metal, which is at the ordinary tempera- 
ture, liquid carbon dioxide is exceedingly cold. 

For purposes of refrigeration, in ice-making and cold 
storage, liquid ammonia is very largely used nowadays ; 
rapid evaporation of this liquid under a suction pump 
gives a very low temperature, and if brine is circulated 
round the pipes in which the evaporation is taking place, 
it is rendered so cold that water may be frozen by it in 
large quantities. 

The success of chemists in liquefying such gases as 
carbon dioxide and ammonia is now overshadowed by 
the greater achievements of the last ten or fifteen years, 
during which period liquid air and liquid hydrogen have 
been produced in quantity. This has become possible 
by the introduction of an altogether new principle in 
gas-liquefying machines — a principle which deserves a 
few words of explanation. 

We regard a gas as consisting of an enormous number 
of separate particles or molecules moving rapidly in all 
directions ; under ordinary conditions the total volume 
of the molecules is very much less than the space in 
which they move — in other words, the molecules are, 
relatively and on the average, not very close to each 
other. When, however, the gas is compressed, the mole- 
cules are crowded together, and they come within range 
of each other's attraction. Each molecule exerts an 
attractive force on its neighbours, and is in turn attracted 

186 



BELOW ZERO 

by them, so that when a highly compressed gas is allowed 
to expand, there fa a social force resisting the separation 
of the molecules which fa involved in the expansion* In 

overcoming this social force work must be done, and 
for the performance of this work heal is required. This 

heat i^ taken mostly from the gas itself, which there- 
exhibits the phenomenon of "self-cooling.* 

All this may be pat more definitely and practically 
fay saying that when highly compressed air is allowed 
to expand through a small nozzle or a porous plug, it 
becomes slightly colder. In the actual machines for 
making liquid air the device fa further adopted of allow- 
ing the expanded and slightly cooled air to circulate 
round the coil of tubing through which the next lot of 
compressed air is approaching the nozzle. In such a 
nerative process the cooling effects are accumulated, 
and the air which circulates through the machine, alter- 
iv compressed and expanded, becomes gradually cooler 
until at length it condenses and drops into a vessel placed 
reive it. 

A vessel which fa to contain liquid air or liquid 

hydrogen must be specially constructed if it is to be of 
any QSC at all. If we were to put liquid air, which boils 
at — H7 Fahrenheit, in an ordinary glass vessel we 
should very shortly Bee the last of itj owing to the heat 
municated through the walls of the vesseL That fa, 
ill fact, exactly what would happen if we put a glass of 
water in a hot-air bath kept at 100 or 500 . Such a 

•on of heat, however, may be very much 

diminished, IS Pn Dewar has shown, by using 

ble-walled vessels sod removing the air from the sp 
be t weeu the walla Sections of two such vessels, a tube 
I a flask, an,- shown in Pig, !). 

is" 



BELOW ZERO 



The importance of removing the air from the space 
between the walls will be realised when it is remembered 
that under ordinary circumstances that space is filled with 
molecules of oxygen and nitrogen rushing hither and 
thither. With the outer wall near the temperature of 

the atmosphere, and 
\ 1 \ ) the inner one in con- 
tact with liquid air, 
these molecules act like 
an army of heat-car- 
riers. Each molecule 
as it strikes the outer 
wall will take up so 
much heat, which 
sooner or later it de- 
livers up to the inner 
wall, only to return 
for a fresh supply. 

When the air is left in 

Fig. 9. — Double-walled glass vessels — so- , 

called vacuum vessels. Owing to the the intervening space 
absence of air between the walls, hot the transfer of heat is 
liquids put in such vessels remain hot, therefore very ra pidly 
cold liquids remain cold, for a remark- * 7 . • 

ably long time. effected, and the liquid 

air in the vessel soon 
evaporates. When this space, however, is rendered free 
from air, the heat-carrying molecules are removed, and 
the inner tube is more perfectly cut off from any heat 
exchange with the atmosphere. The insulation of the 
inner tube is made still more complete by silvering the 
inside of the outer one, for at such a bright surface the 
heat rays are reflected. 

In a Dewar vacuum flask, surrounded by a non-con- 
ducting material like cotton-wool, liquid air may be kept 

188 





BELOW ZERO 



for over twenty-four hours, and the examination of its 
properties ifl thus rendered possible. Not only is it 
possible to study the properties of liquid air itself, but we 
can see how other substances behave when cooled to the 
temperature of liquid air. Their 
behaviour then is frequently quite 
different from what it is under 
ordinary conditions. Grass, leaves 
of plants, and indiarubber, for ex- 
ample, become so brittle when kept 
for a >hort time at the tempera- 
ture of liquid air that they can 
ly be powdered in a mortar. 
An egg, after immersion in this 
wonderful medium, becomes bo 
"hard-boiled" that it may be 
rely knocked about without 
being damaged. Chemicals, too, 
which react vigorously at the ordi- 
nary temperature, become mutually 
callou^ when cooled to the boiling- 
point of liquid air. 

It has just been stated that liquid 
air boils at —'347° Fahrenheit, but 
by boiling under reduced pressure 
the te mp er a ture is lowered to a point at which the air of 

the atmosphere will condense straight away. This may be 

j limply and very beautifully shown in the following 
manner. A Dewar vacuum tube (see Fig. 10), filled to 
the extent of two-thirds with liquid air, is provided with 

a cork. Through this cork there are passed (1 ) so empty 

gla- ed at the bottom and dipping into the 

liqui : (U) i benl tube, B, open at both end* sod 

189 




FIG. 10.— The apparatus 
sketched here serves to 
show the intense cold 
which is produced by 
boiling liquid air under 
diminished pressure. 



BELOW ZERO 

leading to the vacuum pump. When the latter is turned 
on, the liquid air in the vacuum vessel begins to boil 
vigorously under the reduced pressure, and in consequence 
of the low temperature thus produced, air gradually con- 
denses and collects as a liquid in the previously empty 
tube A. That, of course, is the natural result of bringing 
the temperature of the air in A below its boiling-point. 

The composition of liquid air is not quite the same as 
that of gaseous air, for the simple reason that oxygen is 
rather more easily condensed than nitrogen, so that liquid 
air contains a higher proportion of the former. Further, 
if liquid air is allowed to evaporate slowly, it becomes 
very much richer in oxygen, for the nitrogen is the more 
volatile constituent, and passes off more readily, leaving 
behind a liquid with a higher proportion of oxygen. On 
this fact is based a method for the extraction of oxygen 
from the atmosphere. 

More wonderful even than liquid air is liquid hydrogen. 
It is more difficult to prepare, for in applying the 
regenerative cooling process to hydrogen, it is necessary 
first of all to cool the compressed gas to a low temperature 
by means of liquid air before it is allowed to issue from 
the nozzle of the apparatus. Dewar, however, has made 
considerable quantities of liquid hydrogen, and on one 
occasion over a gallon of the substance, made in his 
laboratory, was carried through the streets of London to 
the rooms of the Royal Society. This quantity would 
weigh only about eleven ounces, for liquid hydrogen is by 
far the lightest liquid known to the chemist ; bulk for 
bulk, it is only one-fourteenth as heavy as water. 

Some very interesting experiments have been made at 
these extremely low temperatures on the vitality of 
bacteria and seeds. Typical bacteria were exposed for 

190 



BELOW ZERO 

a number of hours to the temperature of liquid air, but 
their vitality was not destroyed by this treatment. 
Barley and peas have been kept for six hours in (he 
liquid itself, and yet when they were sown subsequently 
in the ordinary way no falling off in the power of growth 
could be detected. 

It is poedUe to get a very high vacuum in a closed 
glasi tube by simply immersing one end of it in liquid 
hydrogen. The boiling-point of the latter is about 
100' Fahrenheit lower than the boiling-point of liquid air, 
and the mere contact of one end of the tube with the 
liquid hydrogen is sufficient to condense the air which it 
contains bo completely that none is left in the upper part. 

The attainment of such low temperatures has raised 
the \ery interesting question as to what prospect there is 
rf ever reaching the u absolute sera." On various grounds, 
chemists and physicists believe that at a certain tempera- 
ture, — 4(i0 3 Fahrenheit, the existence of a gas as such 
would cease to be possible ; the movements of the mole- 
cules, which we have learned to regard as characteristic of 
a gas, would be so paralysed by the intense cold as to stop 
altogether; the chill of death would settle on their 
activity. This temperature is called the u absolute /< TO, "" 

1^ in the eyes of low temperature investigators what 

the North Pole is to Arctic explorers. 

In this connection tb 1908 will be remembered 

as ti. in which helium, the most obstinately 

substance known. WBM reduced to the liquid slate. The 
labour expended in procuring CVCO 10 little as g oui. 
of liquid helium can hardly be appreciated by the lav 
:• r, but it may be mentioned that the preliminaries 

d in the preparation of 16 gallons of liquid air 
and 4£ gallons of liquid hydrogen I By boiling the 

191 



BELOW ZERO 

liquefied helium under reduced pressure the temperature 
of —454° Fahrenheit was reached — only 6° from the 
absolute zero. It might therefore be thought that this 
interesting point was practically within reach, for an 
interval of 6° does not seem a very serious obstacle. At 
these low temperatures, however, an advance of even 1° is 
a very great matter, and it must be confessed that there 
is no immediate prospect of reaching the chilly goal. 



192 



CHAPTER XVII 
CHEMISTRY AT HIGH TEMPERATURES 

IT i not only into the region of low temperatures thai 
h a surprising advance hap recently been made. 
Much has been achieved also in the other direction, 
and it has lately become possible to realise within a 
limited -pace a degree of heat far beyond what can be 
produced with the aid of ordinary fuel alone. This 
attainment of extremes of heat and cold has immensely 
Bed the range of temperature over which the chemist 
can study the properties of matter, and as a result many 
substances, a- well AS new methods of making old 
substances, have been discovered. 

One result of low temperature research, as we have 
. i- that all the known gases have been reduced to 
the liquid state, and in many cases even solidified. 
Similarly, by the recent application of very high tempera- 
ture-, the most refractory solid- have been melted and 

Apart, however, from the extremely high temperatures 

bed by method-, then- ale easily attainable 

te mp eratures at which many substan dinarily 

as stable soU first melted and thru converted into 

No the possibility of changing any substance 
into vapour without decomposing i\ involve it deal; 

for it dm t1 a distillal ion cm be carried out, an 

a metho I and purifying chemical compounds, 

198 n 



HIGH TEMPERATURES 

this is one of the most ancient and valuable laboratory 
operations. When, for instance, a salt solution — in other 
words, a mixture of salt and water — is boiled and the steam 
condensed, it is found to be pure water, perfectly free 
from salt. This operation of boiling and then condensing 
the vapour — " distillation," as it is called — obviously makes 
it possible to separate salt and water, simply because the 
water is easily vaporised, in contrast to the salt. The 
same principle may be applied in numberless other cases. 
Metals, for instance, which are comparatively volatile, 
such as mercury and zinc, may be separated by distillation 
from others, such as copper and iron, which are mixed 
with them and which are much less easily vaporised. 

A rise of temperature, however, not only makes it 
possible to melt and then vaporise many solid substances, 
but it has also the general effect of weakening the bonds 
which hold together the atoms in a molecule. On heating 
a chemical compound the chances are that when a certain 
temperature is reached it begins to break up into simpler 
compounds, or even into the constituent atoms. This 
change is known as decomposition or dissociation. The 
former term is applied to the case in which the atoms or 
simpler molecules, having been once separated by heat, 
show no signs of coming together again on cooling ; they 
have done with each other for good and all. But in 
many cases the interesting observation has been made 
that the separation caused by heating the compound 
molecule is spontaneously reversed on cooling, and the 
compound is re-formed, provided, of course, that the 
atoms or simpler molecules have been allowed to remain 
side by side. The effect of heating such a compound is 
described as " dissociation," and this is followed on cooling 
by an " association " of the separated atoms or molecules 

194 



HIGH TEMPERATURES 

These cases of dissociation are of great interest, and 

there are many common substances which undergo this 
change on heating. Carbonate of lime in its various 
forms — limestone, chalk, and marble — is one of them. 
When heated it breaks up into quicklime (calcium 
oxide) and carbon dioxide. If the latter were left, in 
contact with the quicklime, then, on cooling, re-combina- 
tion would take place, and the carbonate of lime would 
be regenerated. This being so, the reader may ask how 
it i^ possible to convert limestone into lime by heating or 
44 burning" in kilns. The explanation is quite simple, 
for in the lime-kilns the carbon dioxide is constantly being 
removed by the draught, so that when the lime begins to 
cool, the carbon dioxide with which it would gladly have 
combined is not there. 

This interesting phenomenon of a chemical change 
taking place in one direction at a particular tempera- 
ture, and in the opposite direction at another tempera- 
ture, is very well illustrated by one of the common 
methods for obtaining oxygen from the atmosphere on 
the large BCale. There i> a solid compound, somewhat 
similar to quicklime, known as barium oxide, which 
at a temperature of 1100° Fahrenheit or thereabout 
readily take» in more oxygen, forming a new substance 
— barium dioxide. The grip of the latter, however, on 
the extra atom of oxygen is not very secure, and by 
ing the temperature to 1560° it can he so weakened 

is i> released and may be collected. In the 

actual manufacturiii. -ss a current of air is pumped 

into retorts heated to 1:J()() Kahrenheit and contain- 
ing barium oxide, which takes up the i ami allows 
the nitr ogen to pasi on. When the changing is eom- 

pleted, the current of air ii -hut off, and the 

I9fl 



HIGH TEMPERATURES 

which now contain a certain proportion of barium 
dioxide, are connected with a suction pump. The effect 
of this diminution of pressure is the same as that of a 
rise of temperature, and from the engineering point of 
view it is better to alter the pressure than to alter 
the temperature. The barium dioxide accordingly gives 
up the extra oxygen which it extracted from the air, 
and the oxygen so obtained is compressed in steel bottles 
under a pressure of 120 atmospheres and sent into the 
market. The barium oxide may be used over and over 
again in the same fashion, and, theoretically at least, 
a given quantity of this substance should suffice for 
the winning of unlimited quantities of oxygen from 
the air, by alternate association and dissociation. 

The highest temperatures reached in furnaces fed with 
ordinary fuel — the furnaces employed for technical pur- 
poses — lie about 3200° Fahrenheit, but it is possible to 
get a few hundred degrees beyond that with the oxy- 
hydrogen blowpipe. When we feed a coal-gas flame 
with a blast of air as in an ordinary blowpipe, we 
get a very high temperature, but the effect is wonder- 
fully increased by substituting oxygen for air. The 
reason of this is not far to seek. Roughly speaking, 
air consists of one part of oxygen to four parts of 
nitrogen ; the latter gas, although it takes no part in 
the combustion, yet passes through the flame and has 
to be warmed up, thereby absorbing a considerable pro- 
portion of the heat produced by the combustion. In 
the oxyhydrogen or oxy-coal-gas flame the nitrogen 
is not there to dilute the active oxygen, so that the 
temperature reached is very much higher. 

The increased heating effect secured in this way makes 
it possible to melt platinum, and the operation is actually 

196 



HIGH TEMPERATURES 

carried out in the winning of this metal from its ore.-. 

The furnace in which the platinum is melted must 

obviou>lv be of some material whieh has a higher melt- 
ing point still, and quicklime is found to fulfil tills 
requirement. Pipe-clay, when put in the oxyhydrogen 

name, is immediately fused to a sort of glass, while 
gold and silver not only melt, but vaporise into a 
den>e smoke, 

en the temperature^ of the oxyhydrogen or oxy- 
l-gaa flame, however, are comparatively chilly in 
parison with those which are now attainable in the 
trie furnace. Within the last fifteen or twenty years 
the efficiency of this furnace has been .so improved that 
temperatures of 6000* Fahrenheit can be reached, and 
under these conditions many common substances are 
found to behave in a most extraordinary manner. Such 
a furnace oonsists essentially of a hollow box made of 
te non-conducting material, into the cavity of which 
project two carbon rods. An electric arc is established 
between these rods, with the result that an extraordinary 
'heat is attained in the cavity of the furnace. 
\b irafl said in a previous chapter, electricity is gener- 
ated a- a rule in a dynamo, driven by an engine, which 
in its turn depends for its power on the chemical pre 
of combustion. In the electric furnace we merely get 
back tain fraction of the heat which WBB produced 

in the combustion, and the reader might be inclined 

to o the u1m>1<- affair a irasteful cycle n\' op 

moniical it certainly is not, but the- advanl 

in this, that in tb BC furnace the heat, which 

finally ' bed o\< rasiderable 

'1 in a fraction of a cubic foot. Tli< (fleet 
ocally intensified) the temp LB higher, and this 

L91 



HIGH TEMPERATURES 

is of the utmost importance, as it turns out, for certain 
processes. It must be remembered too, that these objec- 
tions on the score of economy lose their force in cases 
where water-power is available for driving the dynamos, 
as it is, for example, at Niagara and in Norway. 

One of the chief difficulties in working at such high 
temperatures as are reached in the electric furnace is 
to find a suitably refractory substance out of which 
the enclosing box may be constructed. Up to a certain 
point quicklime is an excellent material. As its em- 
ployment in the oxy-hydrogen lime-light shows, it is 
not easily fused, and it has further the recommenda- 
tion of being a very poor conductor of heat. This 
latter property was well demonstrated in an experi- 
ment carried out by the French chemist Moissan, whose 
name will always be associated with the utilisation of 
the electric furnace. In one of the lime furnaces which 
he employed, the top consisted of a slab of quicklime 
rather less than 1£ inch thick. The electric arc was 
allowed to play for ten minutes in the cavity below 
the slab, the temperature rising probably to over 5000° 
Fahrenheit. In spite of this, the slab could be handled 
on the outside without discomfort, while examination 
of the lower surface, which had been in contact with 
the arc, showed that the quicklime had actually been 
melted over an area of several square inches. The 
tremendous heat, therefore, which had been generated 
in the cavity of the furnace had been completely kept 
in by a layer of lime 1£ inch thick. 

With bigger currents and more powerful arcs even 
lime furnaces become useless ; the lime fuses and runs 
like water, and ultimately it boils, producing clouds 
of smoke. The difficulty may be partly surmounted 

198 



HIGH TEMPERATURES 

by enlarging the cavity of the lime furnace, and making 
a little platform o\' fc-inch plates of magnesia and carbon, 
arranged alternately. Using a de\ ice of this sort, MoisSai) 
able to study the behaviour of a large number of 
Bdbstanon at temperatures up to 0000° Fahrenheit. 

In the earlier part of this chapter it was said that, 
compared with zinc at least, copper was not volatile. 
Things are quite different, however, at the temperature 
the electric furnace, as appeared from Mois>an\ 
riments. A piece of copper weighing nearly four 
ounce- was put in a carbon crucible in the furnace, which 
was then warmed up for five minutes by a big current. 

ffcer the carat was turned on, dazzling flan 
18 inches long, burst out violently through the openings 

at the end- of the furnace. These flame- were due to 
i>er yapour burning in the air; and it was found after 
the experiment was over that the copper left in the 
furnace now weighed only >> ounces, 1 ounce of the metal 
having b verted into vapour. Similar and equally 

surprising results were obtained with .such refractory 
me' old, and platinum. 

One of the mod surprising things accomplished in 

Ifoissan's electric furnace was the vaporisation of silica. 
Thi sder may already be aware, is 

the OXlde of tin- el'-iiM nl -ilicon, and i> the main con- 

stit- 1 and quart* Indeed, quarts is nearly 

• -ilica. It is melted with tb in the 

1 after seven to eighl minufa 

thrr)iigli the openings as a blni-h H ff \apour — 

rther proof of the really fiervenl beat ^^ 1 1 icl i is 
gen- i this • 

While the electric i e has astonished os by reveal- 

ing the volatili 1 refract 

I!)!) 



HIGH TEMPERATURES 

materials known to the chemist, it has at the same time 
brought to light a number of substances which are quite 
at home at these high temperatures ; indeed it is the 
electric furnace alone which has enabled us to prepare 
them. Among these substances are the carbides — com- 
pounds of the metals with carbon — and it is in the pre- 
paration of one of these, namely, calcium carbide, that 
the electric furnace is most extensively employed at the 
present time. Moissan showed that by heating a mixture 
of pure lime and carbon in the electric furnace calcium 
carbide could readily be obtained, and this is the method 
now employed on the manufacturing scale, except that 
limestone and coke are used as crude materials instead 
of lime and carbon. The use of limestone instead of 
lime does not really involve any difference, for at the 
high temperature employed the limestone loses its carbon 
dioxide and is converted into lime. The other material, 
the coke, is at best a very impure form of carbon, so that 
the calcium carbide obtained in the manufacturing process 
is not a pure product. 

The essential chemical change which goes on in the 
electric furnace during the formation of carbide is an 
extremely simple one. Lime is a compound of two 
elements, calcium and oxygen, but this union is broken 
by the interposition of carbon at the high temperature 
of the furnace. This latter element combines with both 
the calcium and the oxygen, so that these two are sepa- 
rated. The new compounds formed, calcium carbide and 
carbon monoxide, are quite distinct in their properties, 
for the former remains in the furnace in a fused con- 
dition, while the latter is a gas, and escapes at once. 

As the reader probably knows, the characteristic feature 
of calcium carbide is that it gives off an inflammable 

200 



HIGH TEMPERATURES 

ga<, acetylene, on contact with water. One usually 
regards flame and water as essentially antagonistic, but 
here is a case where water is a sine (]U(\ mm in the pro- 
duction of an inflammable gas. The curious action 
between the water and calcium carbide molecules OOnsisI i 
simply in a change of partners. The hydrogen of the 
water unites with the carbon of the carbide, forming 
acetylene, while the oxygen of the water combine- with 
the calcium of the carbide, forming quicklime, which 
promptly slakes in excess of water. 

oetylene, when burned al specially constructed nodes, 

- a very brilliant flame, more like sunlight in it- 
character than any other artificial illuminant. On this 
ground there is much to be said for the use of acetylene 
for lighting purposes. The portable nature of calcium 
carbide, and the ease with which the gas can be obtained 
from this material, are circumstances also which have 
favoured the introduction of acetylene as an illuminant, 

dally in places where electricity and coal gas are 
not available. 

The eag e r ness of carbon to unite with both calcium 

and oxygen at the temperature of the electric furnace, 

illustrated by the formation of calcium carbide, has 

found a recent interesting application in the manufacture 

bosphonis. The chief source of this element is bone 

ish, which consists to S tent of calcium phosphate, 

'>uiid of calcium, phosphorus, and oxygen, [q the 

older p for obtaining phosphorus fmni bone ash, 

it was put through quite a number of distinct operations, 

ith the aid ot the electric fun, inch 

ghtforward plan is feasible, By simply mixing 

die bone ash wit! '1 beating in Mir furl. 

I •iuiii and the I 

801 



HIGH TEMPERATURES 

forming calcium carbide and carbon monoxide ; the 
phosphorus, on the other hand, escapes as a vapour, and is 
condensed under water in the usual manner. 

It is not only in the electric furnace that the high 
temperature of the electric arc has been utilised, but also 
in connection with the interesting problem of the utilisa- 
tion of nitrogen from the atmosphere for agricultural 
purposes. For the fertilisation of the soil large quantities 
of nitrogenous material are required, which are at present 
derived to a great extent from Chili, where extensive de- 
posits of sodium nitrate — Chili saltpetre, as it is called — 
are found. Those who should know best are of opinion 
that these nitrate beds will be exhausted in thirty years or 
thereabout, and hence it was that Sir William Crookes, in 
his presidential address to the British Association in 1898, 
insisted on the necessity of discovering some way by which 
the great store of nitrogen in the atmosphere could be 
made available. The problem is by no means easily 
solved, for nitrogen is very slow to enter into combination 
with other elements. With the aid of the electric arc, 
however, it is possible to induce some of the oxygen and 
nitrogen in the air to unite, forming nitric oxide, which 
in its turn can easily be converted into nitric acid or 
nitrates. This has been known to chemists for a long 
time, but it is only recently that the difficulties in the 
way of making the process a commercial success have been 
overcome. Within the last few years the necessary plant 
for carrying out this process on the large scale has been 
set up in Norway, where power is cheap ; the factories 
there are now turning out large quantities of nitrate of 
lime, suitable for fertilising purposes, and capable of 
replacing the natural nitrate brought from Chili. 

202 



CHAPTER XVIII 
CHEMISTRY OF THE STARS 

FROM a study of the electric furnace and of the 
curious effects which very high temperatures have 
on the various substances known to the chemist, it 

i- but a short step bo a consideration of the conditions 
whkfa prevail on the BUS and other heavenly bodies, 
where Nature herself has concentrated BO much beat 
What IS the constitution of the BUD and stars? Do the 

tents of which they are composed differ from those 
with which we are familiar: How is their condition 
affected by the high temperatures which prevail there ? 
Such are some of the questions which occur to us in this 

lection. 
T<> Mm k and similar inquiries the older astronomy 
had no reply. It displayed a marvellous power of cal- 
culating times and nranonn, of accurately predicting 'he 
movements of the celestial army, but as to the materials 
of whkfa these other worlds were built up, it had nothing 
At one time, indeed, it looked as it" astronomical 
the end of its tether ; it had attained 

h a thorough mastery of the problems connected with 

nts, the rise, and the distances of the heavenly 

idvanoe was to be expected 

in that din md ther no hope that the oon- 

tion of these bodiei would i I by 



CHEMISTRY OF THE STARS 

How different is the outlook nowadays ! Much in- 
formation is available as to the actual elements of which 
the sun and stars are composed, and it may with truth 
be said that we know more about the chemical composi- 
tion of the heavens above than about that of the earth 
beneath. For man, with all his wonderful achievements, 
has scratched only the surface of the globe, and we can 
but speculate about the materials of which the interior 
is composed. It is, indeed, exceedingly probable that large 
quantities of iron exist in the interior of the earth, firstly, 
on account of the fact of terrestrial magnetism, and 
secondly, because the average density of the earth as a 
whole is considerably greater than the average density 
of the crust — pointing to the presence of some heavy 
metallic material at lower depths. But no direct evidence 
is forthcoming as to the actual composition of the interior 
of our globe. 

If a scientist were asked, however, to name some of 
the materials of which the sun is composed, he would be 
ready with an unhesitating answer, and this would be 
the case also in regard to many of the stars. How has 
this come about ? How is it that we can speak now so 
confidently about the constitution of heavenly bodies, 
whose distance is measured in millions of miles, and whose 
very presence in the sky speaks so eloquently of the 
unattainable and the mysterious ? 

We certainly cannot travel to the heavenly bodies in 
order to study their chemical composition, but we do have 
occasional visitors to our planet from celestial spaces. 
These are the meteorites, the falling of which from the 
sky has excited both fear and wonder in the breast of 
man, and the life-history of which scientists so much 
desire to know. Some consider that meteorites are 

204 



CHEMISTRY OF THE STARS 

Btria] in their origin, and have been project ed into 

e from active volcanoes in long-past ages of the 

earth*- history : hut the opposite opinion is most widely 

held, namely, that they are genuine samples of celestial 

matter. 

An inspection of the line collection of meteorites in the 
Natural History Museum at South Kensington will show 
that many of them consist to a large extent of iron, or 
rather of an alloy of iron with a small percentage of 
nickel. Other meteorites contain but little iron, and are 
more like stones in their composition. Altogether there 
onsiderable similarity in the composition of meteorites 

which have fallen at different times and in different 
places, and this uniformity has suggested to some scien- 
tists that most meteorite-, if not all, have come from a 
common source, and are possibly chip- of one heavenly 

iv. 

\.) ingle element has been found in a meteorite which 
i- not obtainable also from te r res tri al SOUfl The 

which occur mosl commonly in these other-world 
chips, in addition to iron and nickel, are aluminium, 
calcium, carbon, magnesium, oxygen, phosphorus, silicon, 
and sulphur, all in a state of combination. Some, indeed, 

of the compound minerals occurring in meteorites are 

<1 it i- curious that quarts, the mosl common of 

—trial minerals, should not be found in meteoric 

The study of the composition of these celestial visitors 

but if i- not from th< in that 

our trustworthy information about the constitution of the 

derived. Ttii information is obtained in 

inch more wonderful fashion; il ed, not on any 

laborab mens, but o 



CHEMISTRY OF THE STARS 

study of the light which comes to us from the heavenly 
bodies, in other words, on the use of spectrum analysis. 

When white light, such as is obtained from the upper 
part of a candle flame, is passed through a slit at the end 
of a telescope, and then through a glass prism, it is seen 
as a strip which is red at one end, violet at the other, 
and between these two extremes passes continuously 
through the various shades of orange, yellow, green, and 
blue. This strip of graded colour is known as a con- 
tinuous spectrum, and it results from the splitting up of 
white light into its various components, which is effected 
by the prism. The apparatus consisting of all the 
necessary parts for the production and observation of a 
spectrum is known as a spectroscope, and this is the 
instrument which has yielded such marvellous results in 
the study of the sun and stars. 

If we were to examine with a spectroscope the light 
given out by a red-hot poker we should see only the red 
end of the spectrum. If the poker were put in the fire 
again and its temperature were raised, the spectrum 
observed would show some orange and yellow as well as 
red, while if we brought the poker to a white heat and 
examined it in this condition with the spectroscope, we 
should see a spectrum perfectly continuous from the red 
to the violet end. Molten iron also would exhibit a 
continuous spectrum, and one can say generally that the 
spectrum of the light emitted by any incandescent solid 
or liquid is continuous. 

It is quite easy, however, to get an incomplete spectrum, 
one which consists only of isolated lines or bands of 
different colours. In order to do that we have merely to 
examine with the spectroscope the light which is emitted 
by an incandescent vapour. One of the simplest spectra 

206 



CHEMISTRY OF THE STARS 



of this kind is obtained by introducing a lit lie common 
salt (sodium chloride), say on the previously charred and 

moistened end of a match, into the non-luminous flame of 

a spirit-lamp or a Bunsen burner. To the naked eve the 



ft* 



-S.»j — - 



£kl'... | 



Xtd 




Oi~+j\ 


f Vettov* Grfn 


BUim Me/ig^ Ho/et 
































B^i^SBIli 




Mtailw 










M. a.-ctf» » 





11- — The spectrin., diagrammatic only, and serves to 

show trum MMIsffltn of dark lines on a coloured 

background. The actual solar spectrum contains an Infinitely 
greater number of lines than are represented here. 

.<• will assume an intense yellow colour, and it* the 

i- directed towards it, tin ftpeetrum is seen 

bo eonaisl of a single yellow line, a- ihown in Pig, 1 ] ; 

the fl i fact, is glTing out only one particular kind 

of light With a firs! instrument, this line turn 

out to be two di4inct tin* (ether, bui this 






CHEMISTRY OF THE STARS 

division is not apparent with an ordinary spectroscope, 
and need not concern us here. 

Suppose now we were to introduce into the Bunsen- 
burner flame some other salt of sodium- — washing soda, for 
example — we should get exactly the same spectrum. This 
is a fact of the greatest significance, indicating that 
whatever be the form in which sodium is introduced into 
the non-luminous flame, its presence is invariably marked 
by the yellow line at a definite position in the spectrum. 
From this simple case the reader will easily appreciate the 
pow r er of detection with which the spectroscope equips 
the chemist. For if the question arises whether a given 
substance contains sodium or not, he has but to introduce 
some of it into a Bunsen-burner flame and see whether 
that incriminating yellow line appears in the spectrum. 
It has actually been found that as little as one ten- 
millionth of a grain of a sodium salt can easily be detected 
in this way. 

Other incomplete spectra, generally more complex than 
that of sodium, are observed by introducing salts of 
various metals into the non-luminous flame of a Bunsen 
burner (see Fig. 11). Barium salts, for example, impart 
a green colour to the flame, and their spectrum is charac- 
terised by a number of green lines ; strontium salts, on 
the other hand, tinge the Bunsen flame a brilliant crimson, 
and their spectrum contains a series of lines and bands 
mostly at the red end. It is probable that every reader, 
perhaps without knowing it, has seen the colours which 
barium and strontium salts impart to a flame, for the 
green and red lights which figure so largely in firework 
displays are produced by adding these salts to combustible 
mixtures containing sulphur. 

For the detection of sodium, barium, or strontium the 

208 



CHEMISTRY OF THE STARS 

reader might think it sufficient to observe the colour 
which a substance Under examination imparts to the 
Bunson lame. So it would be, provided only one of 
the metals was p re se n t ; this condition, how e ver , will 

not always hold good, and when two or more are present 

the colour of the flame will give no certain indication. 

But it is just here that the full value of the spectroscope 
become apparent, far each constituent in a mixture 
eon tributes to the spectrum its own quota of lines, 
uninfluenced by the others which are present. 

This marvellously sensitive spectroscopic method of 
analysis can be applied not only to metallic salts which 
are volatile in the Bunsen flame, but also to substances 
like hydr ogen, which are gases at the ordinary tempera- 
ture, and to refractory metals such as iron. Ingenious 
have been adopted for bringing these into the 
• of incandescent vapour, from which alone we may 
expect to obtain a characteristic discontinuous spectrum. 
H ydr ogen, for example is filled into a glass tube at 
low pr essure, and an electric discharge IS passed through 
the rarefied ga> ; the spectrum of the glowing hydrogen 
i- then found to be characterised by three main lines, 
red, green, and blue respectively (see Pig. 11). To obtain 
the spectrum of iron, on the other hand, the metal or 
ompounds i- placed be t we en the poles of an 

tie. At the high temperature of this dischs 

the iron is partly converted into incandesce nt \apour, 
and its spectrum, containing an enormous number of 

visible. When once the chara cteris t i c ipi 

of the element-, obtained by one or other of the methods 

just del properly mapped out, then 

each line which we observe in any new spectrum i 
be referred I rhicfa i- re s po nsib le tor it. 

o 



CHEMISTRY OF THE STARS 

All this is more or less by way of introduction, and 
we come now to the celestial problem. If a telescope 
is directed towards a star, a nebula, or a comet, and the 
light proceeding from this heavenly body is examined 
spectroscopically, we find, in a certain number of cases 
at least, a spectrum consisting of definite lines or bands, 
and on comparing these with the spectra already mapped, 
we can with confidence affirm that such and such elements 
are present in the far-off heavenly body. A bold step 
this, right out to the confines of space, and yet one 
which is fully warranted by the scientific evidence. 

In the spectrum of a nebula there are bright lines 
which are identical with the characteristic hydrogen 
lines, so that the latter element must be one of the 
constituents of a nebula. The spectrum of a comet is 
closely similar to that of the element carbon, as obtained 
by examination of the blue base of a candle flame ; 
cometary matter, therefore, contains carbon. Curiously 
enough, as a comet approaches the sun, its spectrum 
alters in character, and evidence is obtained that sodium 
and iron also enter into its composition. 

Surprise is in store for us when we come to examine 
spectroscopically the light which comes from the sun 
and the great majority of the stars. Instead of getting 
isolated coloured lines or bands on a dark background, 
we observe a complete reversal of this, namely, dark 
lines on a coloured background (see Fig. 11). 

The explanation of this puzzling phenomenon is best 
understood perhaps by reference to an actual experiment. 
If we were to direct a spectroscope towards an electric 
arc light, in which there is incandescent solid carbon, 
we should observe a continuous spectrum. Suppose 
now that between the spectroscope and the arc light 

210 



CHEMISTRY OF THE STARS 

interpose a Hansen flame coloured yellow by incan- 

ent ^odium vapour, the effect on the Bpectram U 

rather surprising. The continuity of the spectrum ifl 

seen to be broken by S dark line which occupies the 
t position of the bright line in the ordinary Sodium 

is might easily he shown by momentarily 

BDing off the arc light behind. The arc light is 

much higher temperature than the Bunsen flame, 

and what has happened ifl that the sodium vapour in 
tlie latter has absorbed or picked out of* the light from 
the hotter -ource exactly those rays which it itself 
illy emits. The light which passefl on ifl therefore 
bereft of those particular rays, and the Bpectram showi 
the deficiency. 

ie reader must remember that light is a species of 
vibration, and that just as the string of a musical 
instrument will respond alone to that particular note 
out of many which ha- its own pitch, BO an incandescent 
vapour will absorb exactly those rays which it emits. 

ided, therefore, that the source of white light behind 
i- hot enough, the pa-sage of the light through various 

incandescent vapours at a lower temperature will be 

ded by a number of dark lines on the spectrum 
exactly at tho^e positions which bright lines from the 
lws would occupy. 

ii Bpectram, then, consisting as it does of a 

llge number of dark lines on a coloured 1> 
ground, tell- 01 that tl I the BUS is at a white 

thn in unrounded 

an atmosphere of incandescent vapour at a somewhat 

tower temp By comparing the posit f the 

dark line- in the solar ipectrum with the brighl linefl 

in -pectra which I read] l' pped, m learn 

til 



CHEMISTRY OF THE STARS 

what is the composition of the surfs atmosphere — the 
chromosphere, as it is called. Among the elements 
which are thus proved to be present in the sun are 
hydrogen, sodium, calcium, barium, magnesium, iron, 
zinc, and copper. The reader will see that so far as 
the mere elements go, there is nothing very strikingly 
novel about the composition of the sun, but there is 
probably a considerable difference between the earth 
and the sun in the extent to which the elements are 
combined. On the earth the elements just named are 
almost without exception found in the form of com- 
pounds, but at the high temperature of the sun all 
ordinary compounds will have undergone dissociation 
into their constituent elements. It appears pretty 
certain that the temperature of the sun is not below 
10,000° Fahrenheit, in comparison with which the 
electric furnace, our best attempt at producing a high 
temperature, is miserably cold. 

Similar conclusions as to the composition of the stars 
have been drawn from their spectra, and it appears that 
the elements entering into their composition are pretty 
much those with which we are familiar. Astronomers 
have actually ventured a step farther, and endeavoured 
to estimate the approximate temperature of each star 
from the character of its spectrum. This attempt is 
based on the observation that the spectrum of an element 
varies somewhat according to the way in which it is 
vaporised. According as the substance is exposed to 
the action of a flame, of the electric arc, or of the electric 
spark, a different spectrum is produced. The conclusions 
which astronomers have drawn from these observations 
are deeply interesting ; but that is another story. 

A very curious fact in connection with the application 

212 



CHEMISTRY OF THE STARS 

of spectrum analysis has been the discover} of an element 

in the son before it was known on the earth. In lSb'S 
attention was drawn to a conspicuous bright line in the 
spectrum of the son's atmosphere which did not corr e spond 

to a line of any element which was then known. Lockyer 
and Frankland did not hesitate to assert that there must 
be a new element in the sun, and immediately proceeded 
to its christening: they called it " helium" (Greek, t/\io9, 
the -un). 

Thi- is an excellent illustration of the confidence which 
scientists have in the trustworthiness of the spectroscopic 
method, a confidence which in this particular case was 
justified after the lapse of nearly thirty years. In 1895 
William Ramsay, working with the rare mineral 
cfevette, discovered a gas the spectrum of which contains 
a line coincident with the mysterious bright line already 
mentioned. Tin- pa- i-, in fact, helium, and although 
it i- an element of comparative rarity on our globe, it 
appear- to play an important part in the constitution of 
the Km and -tar-. 

Examples of the wonderful detective power of the 

pe might be multiplied. One might quote, for 

in-tance, the discovery of two new alkali metals, rubidium 

and iJTJUnm, by Run-en and KirchhofK some fifty yi 

ago. T bote name- are -o clo-ely a--ociat«d 

with the marvellous development of spectrum analysis, 
He nen lines in the Bpectrum of a liquid ob- 
tained b abating a certain German mineral water* 

v boldly concluded that there was in thi- water lome 
Ay undii dement, and they forthwith pro- 

ceeded to s ea rc h for it. And thi- element, cerium, took 

tiding! Forty torn of the mineral water had to 
be evaporated and operated on ] i much as o 



CHEMISTRY OF THE STARS 

quarter of an ounce of caesium chloride could be collected. 
A splendid tribute this, not only to the sensitiveness of 
the spectroscopic method, but also to the confidence and 
patience of the searchers. 

Among the many problems raised by the spectroscope 
is that concerning the peculiar light of the Aurora Borealis. 
Its spectrum is characterised specially by a bright yellowish- 
green line, which has given rise to much discussion, and 
which for long could not be referred to any known element. 
Again the discoveries of chemists have supplied the clue, 
and it appears that krypton, one of the recently detected 
gases of the atmosphere, is the responsible party. 



214 



TT is 1 



CHAFTEB XIX 

CHEMISTRY AND AGRICULTURE 



IT is becoming more and more obvious as time goes on 
that there is scarcely any department of Nature's 

activity. scarcely any useful art practised by man, in 
which the laws and principles of chemistry are not involved. 
In the delicate processes which go on in our bodies, in the 
roaring of the blast furnace, in the silent growth of the 
tiniest blade of grass, chemical forces are at work, merely 
on atoms and molecules, and yet producing changes which 
in their sum total can be described only as mighty and 
marvellous. The activity of these forces has often remained 
Unsuspected for long ages, and man's skill in many useful 
ait- has been acquired, not from any scientific knowledge 
of the underlying principles, but by long experience 
and practice. 

Agriculture is a case in point. Since Adam delved, 
the art of tilling the soil has been a common occupation, 
and a vast store of practical knowledge of agriculture has 

: gradually accumulated. In these days of competition, 

however, rule-of-thunib methods, handed down from father 
DOt -uflicicnt to command success, and flic aid 

of the chemist has to !><■ invoked We can well imagine 
how ancirnt and hoary Agriculture might the in- 

:on into Hi domain of the modern upstart Chemistry. 
A if it had any light to teach Agriculture why and how it 

Jit to do this and that! Tin- -t niL:u r b' between the 



CHEMISTRY AND AGRICULTURE 

practice of the past and the knowledge of the new age is 
always recurring, and we are slow to learn the lesson that 
the science of the laboratory cannot in the long run be 
kept out of the field, the factory, the workshop, or even 
the kitchen. 

Suppose, then, we consider for a little what chemistry 
has to teach us about the growth and culture of the 
vegetable world, about the yearly marvel of wood and 
field and garden. For it is a marvel. Look at the fields 
in the time of sowing ; they are brown and bare and 
dead. Look at them five months later ; they are clothed 
with an abundant garment of living green or gold. In 
the interval no influence but that of soil and sun, of wind 
and rain, has played upon the seed and the growing plant. 
Whence, then, all this wealth of fresh material ? Is it a 
new creation, or is it an equally marvellous transformation ? 
If the latter, what are the substances which have been 
changed, as by a magician's wand, into stem and leaf and 
flower ? 

Surprising as it may seem, it is only three hundred years 
ago since a chemist of repute endeavoured to show that 
vegetable substances were produced from water alone. The 
experiment by which he sought to prove this was a very 
simple one, and is worth rehearsal. The story shows how 
easy it is for any traveller into the unknown to miss the 
right path. 

This chemist took a willow weighing 5 pounds and 
planted it in a quantity of dried earth which weighed 200 
pounds. For five years he did nothing to the willow 
except water it occasionally. At the end of that time it 
was pulled up and found to weigh 169 pounds 2 ounces. 
The earth in which the willow had grown was dried as 
before, and was found to be only 2 ounces lighter than at 

216 " 




: : " 



Thcv 






fluinc- 
pbotogr., 



CHEMISTRY AND AGRICULTURE 

the start Our chemist therefore die* the conclusion 

that 164 pound- of wood, hark, roots, and Leaves had boon 

produced from water alone ! The experiment was straight- 
forward enough, and at that time, before the composition 
and influence of the air were discovered) it was quite 
convincing. 

-en now, when we know for a foct that the solid pari 
of a plant is largely derived from the carbon dioxide in 
the atmosphere, the average person may find it difficult 
to realise that a gas which is present in the air only to 

the extent of S parts in 1 0,000 should really be respon- 
sible for all this. Hut so it is. Under the influence of 

light, the green colouring matter in the leaves — the chloro- 
phyll, a- it is called — has the power of dealing with the 
bon dioxide which is taken in from the atmosphere, 
liberating the oxygen, and converting the carbon into 
ioufl compounds which form the substance of the plant. 
It is difficult to appreciate the prodigious quantity of 
carbon dioxide which is consumed by the vegetable world 
in this way, but some idea of it may be gained from the 
that an acre of a good wheat crop obtains from the 
atnr in the course of four month J a- much as 

1 ton of carbon. 

Plant-, then, are the great purifiers of the ah ; if il 
ot for their activity in rem o ving the carbon 
dioxide, there would very shortly be an unhealthy 

of this gas in the atmosphere Prom the Lungs of men 

and animah our bouse and faetory chinm- 

huge quantities of carbon dioxide ait being constantly 

poured out, and with all this the \«_ world must 

L It has d thai an 

will dxnit balsa d men, and although the 

en men an leldom in th< 1 1 1 * • 



CHEMISTRY AND AGRICULTURE 

acre of forest, the winds of heaven secure a wonderfully 
rapid and even distribution of the carbon dioxide. 

To be strictly accurate, we must also bear in mind 
the fact that plants resemble animals in contributing 
to the contamination of the air ; they, too, use up oxygen 
and breathe out carbon dioxide. In daylight, however, 
this process of plant-breathing is quite outbalanced by 
the reverse operation — a characteristic of plants alone 
— whereby they give out oxygen and purify the air. 
It is only when they are kept in the dark that the 
action of plants in giving out carbon dioxide becomes 
noticeable. Taken altogether, their services in purify- 
ing the atmosphere quite outbalance what they contri- 
bute to its contamination. 

The fact that a plant is really able, under the stimu- 
lating influence of light, to liberate oxygen from carbon 
dioxide may be demonstrated by a very simple experi- 
ment. A bit of a growing plant — a sprig of mint, for 
instance — is put in a glass tube, which is then filled 
with tap water and inverted in a dish also containing 
tap water. The latter is employed in preference to dis- 
tilled water in this experiment, because it is charged 
to some extent with carbon dioxide. This simple piece 
of apparatus is then exposed to sunlight for several 
hours. It will be noticed that gas bubbles are formed 
on the surface of the leaves, and that these frequently 
ascend and collect at the top of the tube. After a 
few hours have passed the gas which has collected in 
the tube may be examined. To do this, the thumb is 
put on the end of the tube while it is still under water, 
the tube may then be taken out and inverted, the gas 
in this way being brought to the mouth of the tube. 
If a glowing slip of wood is thrust into the gas while 

218 



CHEMISTRY AND AGRICULTURE 

thumb b removed for a moment) it will be relit, 
showing that the gas which was collected was oxygen. 

So much, then, ifl fairly established, that the carlx)n 

dioxide of the atmosphere Ifl taken in by the plant, 

and that the carbon is retained while the oxygen is 

D off Hut chemifltfl have not been able to dis- 

r the actual chemical process to which the carbon 

dioxide i^ subjected in the mysterious laboratories of 

the plant leaf. It is, indeed, certain that water also i> 

involved, SO that the leaves may be said to feed mainly 

on carbon dioxide and water, a simple life diet which 

iuces the most extraordinary results. When we speak 

of the carbon of the carbon dioxide being retained in the 

plant, we must not s up pose that it is actually found in 

that form ; it i> no sooner extracted from the carbon 

dioxide than it pasM^ into some form of combination with 

hyd- nd oxygen, probably formaldehyde in the 

instance. A- to the methods by which the living 

plant subsequently builds up more complicated pro- 
ducts, Mich as starch, sugar, and cellulose, we know very 
little. 

tperiment which convinced the scientists of three 
hundred yi i that vegetable matter could be pro 

1 from alone ha- been shown to be incompl< te 

inconclusive; but we mart admit at the same time 
tha* enter very largely indeed into the com- 

mon of living plant-. Some socculenl vegetables 

contain over !)(> p. ; cent, of their weight of water, 

in tin- dries! period of the year 

will have a- much ai i () per cut. [fwe suppose the 

plai . iter completely removed, the remainder, 

which v call the "dry material" of the plant, 

mbnstiU and partly of incom- 

219 



CHEMISTRY AND AGRICULTURE 

bustible matter. In the combustible part there are 
to be found five chemical elements, namely, carbon, 
hydrogen, oxygen, nitrogen, and sulphur, the first three 
of which are present in by far the largest proportion. 
These three, combined in a variety of ways, constitute 
the woody matter or cellulose, the sugar, the starch, 
and the fats of the plant. Other ingredients of the 
combustible part of the plant are (1) the nitrogenous 
bodies, which contain nitrogen as well as carbon, hydro- 
gen, and oxygen, and (2) the albuminoids, in which 
sulphur is found as well as the other four elements. 

In the incombustible ash of the plant there are also 
five elements found, namely, potassium, magnesium, 
calcium, iron, and phosphorus ; these are essential to 
the life of the plant, and exist in its tissues largely 
as carbonates, sulphates, and phosphates. These con- 
stituents, as well as some others which often occur but 
are not essential, are derived from the soil in which 
the plant grows, so that the nature and composition 
of the soil are all-important factors in the vitality of 
the plant. In order that the reader may get an idea 
of the relative proportions of the water, the ash, and 
the combustible matter in such a common vegetable 
product as meadow grass, the following figures are quoted. 
The crop to which the figures refer weighed 5 tons 
when freshly cut, and produced 1^ tons of hay. Out 
of the 5 tons — that is, 11,200 pounds — of meadow 
grass, 8378 pounds were water, while the combustible 
matter weighed 2613 pounds, and the ash 209 pounds. 

We have discussed the marvellous way in which the 
living plant procures its carbon, but the origin of some 
of the other constituents is also full of interest. Let us 
consider first the nitrogen, which, although it is present 

220 



CHEMISTRY AND AGRICULTURE 

in vegetable tissue only to a small extent) la an important 

and indeed essential constituent. The reader might 

W ip potie that tlie natural source of nitrogenous food tor 

the plant would be the atmosphere, with its rasl stock of 
nitrogen. It is conceivable that the leaves might take in 

and assimilate the nitrogen of the air, just as they deal 
with the carbon dioxide, which is bo much more BCaroe. 

There are some who have supposed that this really takes 

£, hut the bulk of the evidence shows that the leaves 
nerallv are unable to digest nitrogen when it 
i- presented to them in the form of the element itself 

Atmospheric nitrogen, however, does ultimately reach 

the tissues of Millie plants, but by a very indirect road, 

VtA the soil and the roots. Leguminous plants, such 

peas and vetches, are provided with exceptional 

apparatus for assimilating nitrogen, in the shape of 
lings or i% nodules'* on their roots. These nodules 
contain micro-organisms which have the power of ta! 
in atmospheric nitrogen, and BO manipulating it as to 
render it suitable for use as food by the plant. The 

majority of plants, h o wev e r, are destitute of these p 

lants, and are unable to utilise atmospheric 

nitrogen directly ; they appear to find this element most 

lie when it U presented to them in the form of a 

. svich SI a nitrate. Nitrates arc readily taken up 

from the sod by plants, and the nitrogen i- subsequently 

transformed into the oomplei nitrogenous constituent 

the plant tissues by various chemical process^ which at 
ent are not within our Itnowle r power 

of imitation. In comparison with the practical chemistry 

which goes on in the celb of plants, the methods of the 
:iM lie d crude, and he may well fed 

humble in riei of the compli I delicate p • 



CHEMISTRY AND AGRICULTURE 

which are carried out in the wonderful little laboratories 
of the plant. 

All very well, the reader will say, the plant may take 
in the bulk of its nitrogen in the form of nitrates from 
the soil, but how do the nitrates come to be there at all ? 
To understand this it is necessary to remember that the 
atmosphere contains small quantities of nitrogen in the 
combined form, namely, as ammonia, a compound of 
nitrogen and hydrogen, and as nitric acid, which, as 
already stated, is a compound of nitrogen, hydrogen, and 
oxygen. The ammonia in the atmosphere has been given 
off from decaying organic matter, and the nitric acid is 
due to the power of an electric discharge, such as light- 
ning is, to induce the nitrogen and oxygen of the air to 
combine to some small extent. 

Now these two nitrogenous substances, ammonia and 
nitric acid, the one an alkali and the other an acid, 
dissolve easily in water, and are either absorbed by the 
soil direct, or are washed down into it by the rain. 
Quite a large amount of combined nitrogen gets into the 
soil in this fashion, in addition to what is already there as 
the remains of earlier vegetation. Experiments carried 
out at Rothamsted have shown that the total quantity 
of nitrogen carried to the soil by rain in one year is 
between four and five pounds per acre. When ammonia 
compounds get into the soil their latter end is near, for 
there they are tackled by micro-organisms whose object 
in life it is to convert all other nitrogenous bodies into 
nitrates. Since, from the point of view of the plant, a 
nitrate is a much more digestible form of nitrogen than 
any ammonia compound, these nitrifying bacteria are 
valuable agents in the nourishment of the plant. 

Apart from the carbon, nitrogen, hydrogen, and oxygen, 

222 



CHEMISTRY AND AGRICULTURE 

the origin of which we have discussed, the elements which 

are essential to the building up of the plant are derived 
from the -oil itself Compounds containing potassium, 
gneshim, calcium, iron, sulphur, and phosphorus are 
found in the rocks of the earth's cru>t, and it is through 
the breaking down of these rocks that the various in- 
gredient- o\' -oils have been produced, except, indeed, 
the humus, which has quite a different origin. The 
humus is that part of the soil which represents the 
getation of an earlier age; it is organic in 
n, and contains the ruins and remains of the nitro- 
>u- compounds which were built up in that vegetation. 
Hence arises the fertility of virgin -oil from which no 
oops have ever been taken ; it is rich in nitrogenous 
humu-, and i- practically a storehouse of food for the 

first crop which the new settler grows upon it. 

When the crops which grow on a given piece of ground 
loved year after year, the -oil must obviously 
become impoverished in the chemical materials on which 
the crops have fed 'There need be no anxietv about the 
-npply of carbon; the source of this element is the 
atmo-phere, and fresh quantities of carbon dioxide are 

being produced Nor is there likely to be any 

hydrogen a' vn ; they come from water, 

and not often seriously troubled, in this country 

at least, with a deficiency of that commodity. It i- really 

in regard to nitrogen, phosphorus lime, and pota-sium 
that the -oil I >• BlOSfl rapidly impoverished) and if 

the crops are to be kept up in quality and quantity we 

mu nish th< of the-e elements; that i>, 

airing b essential The n e c e ssity for this 

before the agricultural chemisl 

|)}>earance Mi.- materials 



CHEMISTRY AND AGRICULTURE 

which must be added to the soil have been definitely 
ascertained and their effects on various crops have been 
studied. 

The waste products of the animal body contain much 
of the material which is required for the enrichment of 
the soil, and hence farmyard dung is an excellent general 
manure. Guano, the dried excrement of sea-birds, also 
contains nitrogen, phosphate, and potash, and so has been 
largely employed for the same purpose. Occasionally, 
for special crops and in special circumstances, it becomes 
necessary to supply to the soil a particular plant food — 
nitrogen, for instance. In this case one may use as 
manure either sulphate of ammonia from the gasworks, 
or nitrate of soda from Chili. The nitrogen from 
ammonium sulphate is not so rapidly available for the 
use of the plant as the nitrogen from the Chili saltpetre, 
inasmuch as the ammonia in the former has first to be 
interviewed by the nitrifying bacteria and converted into 
nitrate. 

The approaching exhaustion of the Chili saltpetre beds 
has stimulated chemists to discover ways and means of 
utilising the nitrogen in the atmosphere for plant-feeding 
purposes, and the reader may remember the reference 
made in a previous chapter to the work already done in 
this direction. At the high temperature of the electric 
arc the nitrogen and oxygen of the atmosphere combine 
to a small extent, and the compound so formed is easily 
converted into nitric acid. As already indicated, the 
small amount of nitric acid occurring in the atmosphere 
is to be traced to the influence of electric discharges, so 
that the method now in vogue for the manufacture of 
nitric acid from the atmosphere depends really on the 
production of artificial lightning. 

224 





Vfs /f\ *&" 



., 



Byf*rt>. 

Thi Resul rs 01 Assisi N 

p»cimens of Swedish t I ' iaccnt plot 9 of land. 

In ca^c (./) the plot had been unmanured for many year-: h e plot had 

treated with mineral manure alone min- ral and Qttl anure had 
been u 




I 



ammonium 
except on: 
of lime. 



d l>y the ad 



CHEMISTRY AND AGRICULTURE 

Mention should also be made of another modern 

electrical method of capturing the nitrogen of the 

atmosphere for agricultural purposes. This method 

results in the production of a compound known as calcium 

amide, which readily yields up its nitrogen for the 

>f crops. 

For certain -oils and particular crops H is not necessary 

to manure with nitrate 90 much as phosphate. One of 

simplest way- of supplying this constituent is to grind 

bones and scatter the bone dusl in the soil. Phosphate 

lime, o\' which there is a considerable proportion in 

S an insoluble substance, and as the plant prefers 

to have its food in dissolved form, the effect of bone dusl is 

obvious at once. Such a phosphate manure, howexer, 

be made more readily available by treating the bones 
or other substances containing phosphate of lime with 
sulphuric acid ; this brings some at least of the phosphate 

into a soluble condition, and the product — " super- 
it is called — is extensively employed as 

an ingredient of artificial manun 

It doe- not sound very probable that any product 

ed with a blast furnace could assist the growth of 

plant-, but here again it is the unexpected that happens. 

riuced in presence of lime when molten pig- 
iron containing phosphorus is subjected to a blast of air, 
and so purified, is relatively rich in thai element. It is 
used to a large extenl as a phosphate manure, 
which purpose it must be vet] finely ground 
Bs ititicial addition- to the Boil as the foregoing 

able to stimulate the growth of the plant, 
we must not run away with the idea thai we 
of the situation. Although the proc luYh 

go on darn growth <>f a plant leem to be purely 

t 



CHEMISTRY AND AGRICULTURE 

chemical changes, the fact stares us in the face that we 
cannot turn out a plant in our laboratories ; the thing is 
absolutely beyond us. The attempts so far made to 
imitate the processes of plant growth can scarcely be 
called successful, and our failure seems to be most com- 
plete in connection with the most important and wonderful 
process of all, namely, the assimilation of carbon dioxide. 
The chemistry of plant life and growth is, in fact, one 
of these mysterious chambers which have as yet been 
only partially explored. In spite of failure, however, to 
imitate the actual processes of growth, chemists have 
been wonderfully successful in producing by artificial 
methods the substances which are found in plants. The 
story of the interesting advance that has been made in 
this direction will be told in another chapter. 



226 



CHAPTER XX 
3UGAB AND STARCH 

CHEMISTRY is an all-pervading science. Its scope 
ifl not confined to the laboratory or the chemical 
factory. There is a chemistry of daily life as 
well as a chemistry of the Stan ; a chemistry of foods as 
well as a chemistry of tire. We have already seen that 
many common phenomena really depend on the operation 
of chemical principles, and chemistry has a good deal 
iy ako about our food and the changes which it 
undergoes. 

Sugar and starch are two of the main components of 

our food, and belong at the same time to an interesting 

of chemical compounds known as u carbohydrates." 

Each member of this class contains the elements carbon, 

hydr ogen, and oxygen, and the characteristic feature, to 

which reference is made in the part hydrate of the word 
"carbohydrate," i- that the proportions of the hydrogen 

and tlu- QXygei] aie the same as in water. 

Hie Constituent! of our food l>elong to one or other of 

the three c carbohydrates, tat-, and proteids or 

.minoids. The last -mentioned include all the nitro- 

OOS products, a certain proportion of which is essential 

to the health of the body. Mosl ordinary food-stllffi do 

belong exclusively to one class, but arc mixture*,. 

\Vh« .. for instant tin 9 pea cent, of proteid . 

1 p» fat-, and 74 per cent, of caiboh 



SUGAR AND STARCH 

mostly starch ; in addition, there is about 15 per cent, of 
water and a little mineral ash. As another example of 
a common food, we may take potatoes, which contain 
75 per cent, of water, 21 per cent, of carbohydrates, and 
2 per cent, of proteids ; they contain only a trace of 
fat. The pea differs from the potato in having a 
relatively large proportion of nitrogenous substances — as 
much as 22 or 23 per cent. — while the carbohydrates 
amount to about half the weight of the pea. Cheese, 
again, is a case of a food containing very little carbo- 
hydrate and a high proportion of proteid ; an average 
composition is 34 per cent, of water, 28 per cent, of 
proteid, 33 per cent, of fat, and 2 per cent, of carbo- 
hydrate. As opposed to these mixed food-stuffs, sugar is 
a pure carbohydrate, and butter is practically nothing 
but fat with an admixture of water. 

All carbohydrates are ultimately obtained from the 
vegetable kingdom, and of the numerous substances which 
belong to this class, none is better known than sugar. 
It must, however, be pointed out at once that the meaning 
which the ordinary person attaches to "sugar" is not 
quite what the scientist understands by it. The chemist 
speaks of " sugars," for there are several distinct substances 
known to him which go under this name ; there are, 
for instance, cane sugar, milk sugar, malt sugar, and 
grape sugar or glucose. To these the reader might 
be inclined to add beet sugar, but this would be a 
mistake. The substances just mentioned are indeed named 
from their different sources, but it is not on that account 
that they are regarded as distinct members of the sugar 
class. Investigation has shown that they are chemically 
different ; even although in some cases the proportions 
of carbon, hydrogen, and oxygen are equal, the arrange- 

228 



SUGAR AND STARCH 

mcnt of the atoms in the molecules ia not the same. The 

sugar, however, which IS obtained from the beet 18 
chemically identical with that which comes from the 
r cane ; beet sugar, in fact, 18 Simply cane sugar from 
another source. 

What we refer to in ordinary conversation as "sugar,' 1 
the article which appears on the breakfast- and the tea- 
table, is cane sugar, although in reality a groat deal of 
it has been manufactured from beetroot. The inhabi- 
tants of these islands ought to be specially interested 
in this article, for the annual consumption per head of 
the population of Great Britain is about 80 lbs., which 
juivalent to eighteen pieces of ordinary lump sugar 
per diem. This i> nearly three times as great as the 
corresponding figure for France or Germany. 

Up till a hundred years ago there was practically no 

sugar produced except from the sugar cane, whereas now 

more than half the world's production of sugar is derived 

from t) : the name "cane sugar,"* therefore, is 

not quit accurate a description of this compound 

• once was. Much energy has been devoted to the 

atific cultivation of the beetroot, and to the proper 

action of the sugar which it contains. The advance 

which 1 made in this way is very well illustrated 

ome published figures showing that whereas in 1886 
a ton of 1) yielded 124 lbs, of sugar, the same 

tity in 1871 was made to yield L>04 lb-., in L900 

:u\ 

In the old methods of extracting sugar from the canes, 
crushed, and thejuice which was thus pn 
out 1 and then boiled down until the sugar 

rtallised. Another and modern plan, which is similar 

to tl from beetroot-. 



SUGAR AND STARCH 

is to immerse the canes in water and soak out the sugar. 
The juice obtained in this way is then concentrated to 
its crystallising point. The crystals are not pure, and 
are spoken of as "raw" sugar; the uncrystallisable juice 
which is separated from the crystals — uncrystallisable 
because of the mixture of substances which it contains — 
is used as food in the form of treacle or molasses. 

Although a good deal of raw cane sugar finds its 
way into the market as "Demarara," the bulk of it is 
first refined. The process of refining consists in dis- 
solving the raw sugar in water, filtering the brown 
solution through cotton bags, and then decolorising it 
by keeping it in contact for some hours with animal 
charcoal. 

Contrary to what one might expect from the name, 
animal charcoal contains only one-tenth of its weight 
of carbon. It is got from bones in the same way as 
coke is obtained from coal, that is, by heating strongly 
in a retort. The organic matter in the bones is charred 
by this treatment, and the resulting carbon is distri- 
buted in a finely divided condition over the phosphate 
and carbonate of lime which constitute the bulk of the 
mass. 

In this state of fine division the carbon has the re- 
markable property of absorbing any colouring matter 
from a solution with which it is left in contact for a 
time. Red wine, for instance, if shaken with animal 
charcoal and then filtered, runs through as a colourless 
liquid, like water. A coloured sugar solution is similarly 
affected, and pure sugar is then obtained by concen- 
trating the decolorised liquid to the crystallising point, 
as already described. It is somewhat startling to reflect 
that a heap of uninviting-looking bones may be destined 

230 



SUGAR AND STARCH 

to purity our best lump sugar, but this is frequently 

the c 

The reader need not trouble himself much about milk 
sugar, which forms S per cent, by weight of ordinary 
milk, or about malt sugar, which is formed from grain 
in the preliminary stages o( brewing beer; but grape 
sugar or glucose is quite an important carbohydrate, and 
is worth a little attention. The very name suggests one 
of its louiees, and as a matter of fact grapes contain 
19 percent of glucose; the percentage present in dried 
fruits i> much higher, and in tigs is over 50, 

The bee must not be forgotten as an agent in the collec- 
tion of glucose, for honey contains 70 to 80 per cent, of 
this sugar. It comes originally, of course, from the flowers, 
and an estimate of the sugary matter in these has shown 
that the bees must visH several hundred thousand heads 
in order to collect one pound of honey. We pride OUT- 
selve-, and justly, on the methods by which minute 
amount- of a precious metal can be extracted from large 
massi ! of rock and earthy material, but the remarkable 
achievement of the bee in the accumulation of almost 
m icrosc o pic quantities of sugar is probably unequalled. 

Glucose is not nearly so sweet as cane sugar, yet in 
the olden days, before cane sugar had been introduced, 
honey was the material used in sweetening dishes for 

table. Later on, glucose was obtained from grapes, 

but nowadays it is made by boiling starch with dilute 

sulphuric acid; it is then known ncfa sugar/ It 

t be admitted that the names of the various sug 

are a little confusing; already we b D that I 

sugar i- the same _ r, now it appears that 

nothing else than grape sugar. 

XI 1'iired for the manufacture of glucose by 



SUGAR AND STARCH 

this method is generally derived from potatoes or maize ; 
it is made into a cream with water, and then run into 
boiling dilute sulphuric acid. In these circumstances the 
starch undergoes a gradual change, which the chemist 
describes as " hydrolysis," and the boiling is continued 
until starch can no longer be detected in the liquid. 
The test is made by taking a sample out of the boiler, 
cooling it, and adding a little iodine, which gives a blue 
colour so long as unchanged starch is present. Possibly 
the reader may at some time or other have accidentally 
dropped a little tincture of iodine on a starched article, 
say a shirt-cuff, and noticed that a deep blue stain was 
produced. This is a very characteristic peculiarity of 
starch, and always serves for its detection. 

The solution of glucose obtained after hydrolysis is 
complete must, of course, be freed from the acid, which 
would be a most undesirable constituent of any food-stuff. 
The cooled liquid is accordingly neutralised with chalk 
or whiting, and the insoluble sulphate of lime which is 
formed is filtered off. It is further necessary to de- 
colorise the solution by means of animal charcoal, and 
to concentrate by evaporation until the solid can be 
obtained. 

The glucose produced in this way will be a white sub- 
stance, provided sufficient care has been taken to de- 
colorise the solution thoroughly by animal charcoal ; 
otherwise the substance will have a light brown tinge. 
If the conversion of the starch should have been in- 
completely carried out, then a liquid glucose syrup is 
finally obtained, which, although not so pure as the solid 
glucose, may be used, and is extensively used, both in 
confectionery and brewing. 

Other carbohydrates as well as starch can easily be 

232 



SUGAR AND STARCH 

converted into grape sugar. Cane sugar itself is changed 
into glucose and another similar sugar called M fructose," 
ely by heating a solution with an acid sulphuric acid, 
mple; the cane sugar is said to be u inverted, * 
and the resulting mixture of glucose and fructose is 
known as "invert sugar. 11 This product ifl obtained in 
the form of a thick syrup, and ifl extensively employed 
in brewing. 

Thi- reminds one that it was the use of sulphuric acid 
in the manufacture of glucose and invert sugar which led 
to the u arsenic in beer"" scare of 1900. In Manchester 
during that year a number of cam of arsenical poisoning 
occurred, and were ultimately traced to the beer drunk 

by the patients. Arsenic was found also in the glucose 

and invert sugar from which the beer had been brewed, 
having got into these materials from the sulphuric acid 

d in their manufacture. It must be remembered 
that the sulphur required for making sulphuric acid is 

rally in the form of iron pyrites, a natural product 

which is invariably contaminated with arsenic. Unless, 

tin r lbmitted to special purification, commercial 

sulphuric acid i^ liable to contain arsenic ; and it was the 

och an impure acid in the manufacture of glut 

and invi _ r that was at the bottom of the "arsenic 

in b er " troub 

Toe convi ther carbohydratefl into gluo 

can be broughl about by certain ferments without the 
aid' at all. When moisl barley, for insl 

alio Hi (] ** diastasf " is | 

Ulifl subtle agent upsets the equilibrium of the 

culefl in the barley. Under its influence they 

are i d into sugar molecules, and the latter, unlike 

starch, can be f mo]. 



SUGAR AND STARCH 

Again, the conversion of starch into sugar is a chemical 
change of which the reader himself is the scene. As 
already pointed out, much of our common food contains 
carbohydrates, and of these starch is the one which is 
present in the largest proportion. Now starch itself con- 
sists of fine granules which are insoluble in cold water. 
On this account any form of starchy food should first be 
boiled, or baked in the presence of moisture. This treat- 
ment secures the bursting of the granules ; they are dis- 
solved or at least softened, and are so rendered amenable 
to attack by the digestive juices. This attack begins in 
the mouth, where a ferment, lying in wait in the saliva, 
begins the conversion of starch into sugar, a process 
which is completed by the juices in other digestive 
organs. 

This important ferment in the saliva is not developed 
until several months after birth ; the disadvantage, there- 
fore, of giving starchy food to infants will be apparent. 
If such food is given it is not assimilated, for all other 
carbohydrates must be converted into glucose if they are 
to be made available for the nourishment of the body. 
For the further utilisation of the glucose the liver is 
responsible, and if this organ is not doing its duty, the 
sugar goes through the body unchanged and unassimi- 
lated ; the presence of glucose in the urine is, in fact, 
taken as evidence of diabetes. In cases of this disease 
the patient should abstain from the use not only of sugar 
itself, but also of all starchy food-stuffs, for these latter, 
as we have seen, are rapidly converted into glucose by 
the digestive juices. 

Another interesting carbohydrate which is worthy of 
mention is dextrin, or British gum. This compound is a 
sort of half-way house between starch and glucose, and is 

234 



SUGAR AND STARCH 

formed when starch IS heated either alone or with a little 
acid. Although dextrin has the same chemical composi- 
tion as starch, it gives a reddish brown colour with iodine, 
instead of the blue colour which is BO characteristic of 
starch. Dextrin is applied to some curious purposes — 
mple, as an adhesive on envelopes and postage 
stamps, in giving a gloss to paper and cardboard, and 
in producing a head on beer and Berated liquids. 

The possibility of converting the various carbohydrates 
into glucose is further illustrated by the changes which 
table fibre, or cellulose, may be made to undergo. 
This is a carbohydrate of the same chemical composition 
BS March, but differs from the latter in being indigestible 
except by he rb iv o rous animals, which have a special 
apparatus for dealing with it. Cotton-wool and Swedish 
filter-paper are nearly pure cellulose, from which it will 
be obvious that this carbohydrate is not a suitable article 
far human food. When eaten, it simply passes through 
the body without being digested. 

in either of the forms just mentioned, is 

1 by strong sulphuric acid; if the solution i- 

diluted with water, and subjected to prolonged boiling, 

cellulose, like starch, only leSB readily, is co n verted 

into glucose. Bearing in mind that the fei mentation of 

this sugar yields alcohol, the reader will perceive that it 

hially possible to prepare spirituous liquors from linen 

for these consist very largely of oellul 

alcohol, how eve r , is s transformation which 

1 curiosity rather than a practically applied 

: 

T " cellulose " suggests the commercial article 

which is indeed derived from 

cellule ... in (. .\. it was thown thai when cotton- 



SUGAR AND STARCH 

wool — that is, cellulose — is treated with nitric acid, the 
explosive gun-cotton is obtained. If a weaker acid is 
employed, and the time during which it acts is shortened, 
another compound is produced, intermediate between 
cotton and gun-cotton. This product, when mixed with 
camphor and properly worked up, is celluloid. Although 
not explosive like gun-cotton, it is highly inflammable, 
and numerous burning accidents have been caused by the 
ignition of combs made of this material. 

Attempts have been made to render celluloid un- 
inflammable, but this can be done only by sacrificing 
some of its valuable properties. One of these is its 
plasticity ; separate pieces of celluloid, when heated to a 
temperature a little above the boiling-point of water, can 
be welded together by pressure, just as two pieces of 
red-hot iron are welded under the blacksmith's hammer. 
Then, again, celluloid can be planed, carved, or turned 
on the lathe, and the appearance of the articles so pro- 
duced leads to its name of "artificial ivory/ 1 It is em- 
ployed not only in combs, but in the manufacture of such 
various things as piano keys, billiard balls, dolls, and 
photographic films. 

At the beginning of this chapter carbohydrates were 
spoken of as important constituents of food, but it will 
now be evident that this important class of chemical com- 
pounds figures largely in common life apart from food- 
stuffs. They are to be detected in our stationery, in our 
clothes, on our postage stamps, and indirectly in celluloid 
and the many useful articles which are made of this 
material. 



236 



CHAPTER XXI 
PATS AND OILS 

THE romantic element about suet, candles batter, 
soap, and linseed oil Lb, it must be co nfe ss e d, not 

particularly prominent, and yet there is perhaps no 
- of natural products which ministers in a more won- 
derful and varied fashion to the needs and comforts of 
man than the tats and oiK Versatility in an individual, 
the ability to do half-a-dozen things of the most di\- 

iption is always interesting, and the study of the 

in which the stream of natural products is diverted 

by the wit of man into all sorts ot" useful channels is 

urinating, if not romantic. 

Fats and oiK are natural products, their name is legion, 

and there is an inexhaustible supply. The oils, however, 

with which we ^hall chiefly deal in this chapter, are those 

which can Ik- described as liquid fats. There will indeed 
be a bra to the 10-caUed "mineral* oils, which 

are de ri ved from the petroleum springs of Russia and 

]y described in chapter \ii., but the 

M volatile "* 01 ** e^eiitiul" oil-, like oil ot nulling OT oil 
of lemon-, will l>e left out of account, at lea-t for the 

present. 

It QO of the mineral and the 

essential oQs, we i • thai the numerous fats and 

oil- derived from l>oth the animal and tip I ible 

kingdoms an remarkablj similar in chemical composition, 

S 



FATS AND OILS 

however diverse their origin. A fat or fatty oil is a 
substance analogous to a salt, which, as already shown, is 
a neutral compound produced by the combination of an 
acid and a base. The constituent of the fats and oils 
which corresponds to the base of a salt is glycerine, while 
the acid is very often stearic, oleic, or palmitic acid. 
The compound formed by the union of glycerine and one 
of these " fatty " acids is termed a " glyceride," and the 
commonly occurring fats and oils are to be looked on as 
mixtures of different glycerides. 

That fats and oils are obtained from an extraordinary 
variety of sources is shown by the fact that hogs' kidneys, 
cotton seed, milk, hazel nuts, cod livers, and cows 1 feet, 
are among the raw materials requisitioned for the purpose. 
Fats and oils of a vegetable origin are obtained mostly 
from fruits, which in some cases contain a high pro- 
portion of fatty material. The fruits of the olive tree 
contain about half their weight of oil, used, for instance, 
in packing sardines, while in the seed of the flax plant 
there is 30 to 35 per cent, of oil, familiar to every one as 
linseed oil. 

A vegetable oil is extracted from the seed in one of 
two ways. The seed is either crushed under pressure, so 
that the oil is squeezed out, or it is heated with some 
volatile liquid such as petroleum or carbon disulphide, which 
dissolves out the oil and can afterwards be boiled away. 
When the first method is employed the expressed oil is 
collected in suitable vessels, and the compressed residue, 
still containing a small proportion of oil, is sold as oil- 
cake for feeding cattle. This way of utilising the 
residue is obviously an economical one, for the unextracted 
oil is ultimately recovered from the cow or bullock in the 
form of butter, tallow, or neatVfoot oil. 

238 



FATS AND OILS 

The process most in vogue for obtaining animal fats 
and oilfl is known as u rendering w ; the fatty matter is 
boiled with water or steamed, and the oil which floats 
on the surface is removed. In this way it is obtained 
free from adhering tissue. 

Attention was drawn in the previous chapter to the 
fact that fats are one of the principal constituents of 
human food. Butter, lard, suet, olive oil, and cocoa 
butter may be mentioned as fats which are Used either 
directly a- food or in the preparation of dishes for the 
table. In this country we import over ^20,000,000 
worth of butter alone per annum, in addition to the 
butter made and consumed at home. 

Butter, however, is not the only fat which is used 
directly as human food. Margarine, an artificial mixture 
of animal fats, with possibly a small amount of vegetable 
fat, i- manufactured in large quantities nowadays, the 
annual consumption in this country being estimated 
about £5,000,000 worth. Its manufacture dates back 
to the time of the Franco-German war, when the inhabi- 
tants of Pari- were hard up for butter. This fact would 
seem to indicate that margarine is to be used only by 
those who are reduced to their last resource-, but really 
no reasonable objection can be taken to this material 
D made under Batisl conditions and -old under 

it- own name. A member of Parliament, referring on 
one occa>ion to margarine, spoke of M all the 
rubbish of the world which is being dumped down in thi- 

com but this de sc ripti on u now quite out of date 

Other edible lata turned out in large quantiti 
K>-caDed vegetable butters, which sre valued by our 

vegetarian t I appear in the market under all 

sorts of fancy In India, where, on religlOUfl 



FATS AND OILS 

grounds, the natives will have nothing to do with animal 
fat of any description, vegetable butter is prepared in 
large quantities from cocoa-nut oil and palm -nut oil. 
The Greenlander, on the other hand, who has no such 
scruples, revels in blubber. 

The preparation of edible butters and oils is only one 
of the many industries which depend on the utilisation 
of fats and oils. If it were not for their disguise, for 
the chemical processes to which they have been subjected, 
we should detect these materials in many an unsuspected 
place. They may be traced not only in the butter on 
our bread, but also in the candles which light our tables, 
on the artist's canvas, in the linoleum on our floors, and 
in the "matchless cleansers" which delight the house- 
wife's heart. 

The chemical processes which have been referred to 
as disguising the obvious characteristics of fats and oils 
are not all carried out by the manufacturer. There is 
one class of oils, the so-called " drying " oils, the value of 
which is due actually to their own instability and to their 
sensitiveness to atmospheric influences. Common linseed 
oil, obtained from the seeds of the flax plant, is the 
typical member of this class. 

If a film of linseed oil is exposed to air it absorbs 
oxygen with great avidity, becoming gradually more and 
more sticky and viscous during the absorption, until at 
last it dries to an elastic skin. The amount of oxygen 
thus absorbed by the oil may be as much as twenty per 
cent, of its weight. In this respect linseed oil is abso- 
lutely different from, say, olive oil, which remains liquid 
however long it is exposed to the air, and is therefore 
described as a " non-drying " oil. 

The complete drying of a thin layer of linseed oil 

240 



FATS AND OILS 

occupies about three days, but the process may be con- 
siderably accelerated by a certain device, as was shown 
long ago by a Dutch artist lie Pound that it' the 
ordinary or raw linseed oil were previously healed to 

a high temperature with lead oxide, the time required 
tor drying was shortened to six or eight hours - an 

observation which has turned out to be a \ery valuable 
contribution from art to practical science. 

At tlu' present day linseed oil which is to be used in 

the manufacture of paints fa subjected lo a preliminary 

tment of the kind suggested by the Dutchman, the 

only differences being that the temperature now employed 

is not so high (only about 800 Fahrenheit), and other 
" driers " besides lead oxide may be used The product 

is known as "boiled*" oil, although, si rid ly speaking, it 
never been boiled at all, but only heated; fatty oils 

would, as a matter of fact, decompose if we al templed lo 
lx)il them. The name M boiled " oil is one of those little 

curacies of terminology which one comes across 

-ioiially in the technical world -a " terminological 

inexactitude,* the politicians would call it. The i 

undid to M black had," which, as the reader will have 
1 from chapter V., contains no lead at all. 

As already indicated, boiled oil is extensively used 
in the preparation of paints and varnishes. The colour- 

Merial, while had, lampblack, ul f ramarinc, or 
red lead, as the case may be is first ground with a 

;1 quantity of linseed oil and then mixed with more 
oil, generally of the boiled variety, and with oil of 
turpentine When a layer of the paint is spread on a 

siirfacr of metal Of wood it dries quickly, and a pro- 

:w skin is Left, Th. drying of wet paint, the reader 
will now perceive, is quite different from irhal f 

'M Q 



FATS AND OILS 

place when a newly washed cloth is hung out on the 
clothes-line. In the latter case simple evapbration of 
water, a purely physical process, takes place, while the 
drying of paint involves a chemical change, the com- 
bination of the oil with oxygen from the air. 

Like the painter, the glazier depends on the drying 
qualities of linseed oil when he fixes up a new pane 
of glass with putty. This dough-like material is obtained 
by grinding up whiting with linseed oil, and it is the 
latter ingredient which is responsible for the gradual 
hardening of the mixture on exposure to air. 

This curious drying power of linseed oil is made to 
contribute to the equipment of our houses, not only 
in paint, but also in linoleum. Linseed oil is the raw 
material of the linoleum manufacture, and the first 
operation in the factory is the drying of the oil on a 
large scale ; this is effected by hanging up sheets of 
textile material and allowing the oil to run slowly 
over them ; under these circumstances it dries gradually 
to a tough, gelatinous mass. This oxidised and solidi- 
fied linseed oil is then mixed with rosin and ground 
cork, spread on a canvas backing and sent into the 
market as linoleum. 

One purpose for which drying oils are obviously 
not suited is lubrication. If linseed oil were put into 
the bearings of a machine, it would get viscous and 
tough in the manner already described, and the running 
of the machinery would be hindered instead of helped. 
For lubricating purposes a non-drying oil is required, 
such as tallow oil, lard oil, neatVfoot oil, olive oil, 
rape oil, or castor oil. The metallic variety of palm 
oil, which travellers frequently find necessary to stimu- 
late official activity or to produce temporary blindness 

242 



FATS VXD OILS 

in the official eye^ might be classed as a lubricant, 
but the naturally occurring variety, which, by the way, 
h a solid, not a liquid, finds only a limited applica- 
tion in this direction. 

The use of' tatty oils for lubricating purposes has 
; greatly restricted in recent times by the intro- 
duction of mineral Oils, obtained from petroleum 
Wells. It must be borne in mind that the fatty oils 
are compounds of glycerine and an acid, and that under 
on conditions— when exposed, for instance, to the 
action of high-pressure steam — they may be split up 
into these constituents, This means that the use of 

a lubricating fatty oil may lead to the formation of 

free acid on the bearings, a result which, in view of 
the corrosive action of acids on metals, is highly un- 

\ I objection of this sort can be ui 
nst the petroleum or mineral oils, for these are 
limply hydrocarbon-, compounds of carbon and hvdro- 

1 ;i- such are unaffected by air or -tram. Hence 

it comes that for lubricating purposes fatty oils have 

: largely displaced by mineral oils. As a matter 

of tact, most of tin- lubricating oils used at the presenl 

time arc mixtures of the two varieties, 

The discovery of petroleum has very notably lv- 

: the use of tatty oils in another direction, namely, 

in their application as ilhnninaiiK It is not bo very 

paratlin oil was a nowlty, and up to 

that t;: .'• Oils, Mich as oliw and rape oils, 

ly employed ai lourcei of light Nowads 
we may my with confidence, the private individual d 
nothing excepl paraffin as t burning oil. It is t li«- 
which furnish the mod conspicuous example 
of i .» the old custom, the lamp I on 



FATS AND OILS 

signals being still fed with rape oil. In lighthouses, 
too, there is a certain extent of adherence to the old 
kinds of burning oil, inasmuch as whale and seal oil 
are largely employed in the lamps ; it is true these 
are animal oils, in contrast to olive and rape oils, but 
they belong to the same class of chemical compounds. 

Fats and oils are made available for illuminating 
purposes not only directly, in the way just described, 
but indirectly also, after being subjected to chemical 
treatment by the manufacturer, and being made to 
yield up the fatty acids which they contain in com- 
bination with glycerine. In connection with the subject 
of lubrication it was said that under the influence 
of high-pressure steam a fatty oil might be decom- 
posed into fatty acid and glycerine. Now, although 
this may be undesirable behaviour in the case of a 
lubricant, yet it is precisely the change which the manu- 
facturer brings about on a large scale in order to pro- 
duce candles. 

Our forefathers, it is true, used unchanged fats in 
the manufacture of candles ; we have all heard of " tallow 
dips," and the " snuffers " which went along with them. 
Tallow is the rendered fat of cattle and sheep, and con- 
sists chiefly of two fatty acid glycerides, those of stearic 
and oleic acids, together with a small quantity of the 
glyceride of palmitic acid. The mixture is easily melted, 
and the " dip n was made by repeatedly dipping a cotton 
wick in molten tallow. 

The wick in a modern candle, on the other hand, is 
made of yarn, plaited in such a way that the end of 
the wick bends over and is burned at the side of the 
flame, as the reader has doubtless observed himself. 
Such a wick cannot be employed in a tallow candle, 

244 




38 






g B 



_ 



8 1 






3£ 



2=5 







FATS AND OILS 

rthe curving over of the end of the wick would shifl 

hi lower portion out of the centre of the candle, tallow 

ing such a plastic material. The end of the wick 

in a tallow dip keeps straight, and 90OD gets into the 

p of the flame, ^hcre it is charred, hut cannol gel 

oxygen for complete combustion; il interf 

with the proper burning of the candle and the flame is 

rendered dull and smoky. From time to time, therefore, 

the tallow candle must be "snuffed"; that is, the end 

of the wick must be removed. 

When tallow fa treated with hi<jh-prc»ure steam it 

il split up, or u hvdrolysed," lo use the teelmieal term, 

and the three acids mentioned above are liberated from 

(he glycerine. At this stage they are crude 

and dark in colour, and are therefore subjected to dis- 
tillation in a current of superheated steam. 'The nearly 
irless mixture of the purified acids obtained in this 
i- subjected to pressure, so that the liquid oleic 
Mpieczed out; the remaining product, known as 

and consisting mainly of stearic acid. i> cast 
lies in suitable mould-. 

does not melt below l(j() Fahrenheit, 

thai candles made of thi- material will keep erect 

in tropical countries. For use in temperate climal 

usually mad<* of a mixture of stearine and 
paraffin wax, the latter being obtained in large <juantiti< 
(about £4,000 tons a year) by the destructive distillation 

of Scottish -hale. Candle- i matter of tact, in 

from paratl'm wax alooe, hut tiny are rather -oft and gives 
oflapsing in hot weather. Tin- tallow candle fa 

• d from the market by these modern com- 

Onual output of the former in 

country amount- to a u r( »<»d many hundred tons. 



FATS AND OILS 

In addition to tallow, stearine, and paraffin wax, 
beeswax also is used in the manufacture of candles. 
From the chemist's point of view, beeswax is quite 
different from paraffin wax, but similar to tallow ; like 
the latter, it is analogous to a salt, and results from 
the union of fatty acids and an alcohol, only in this 
case it is another alcohol than glycerine. 

The hydrolysis of a fat or oil into glycerine -f fatty 
acid is effected, as we have seen, by the action of super- 
heated steam. By a modification of this procedure we 
can obtain glycerine + soap instead, for a soap is nothing 
more than the sodium or potassium salt of stearic or 
palmitic acid. For the production of soap, therefore, 
the fat, instead of being treated with superheated steam, 
is boiled with caustic soda or caustic potash. If soda 
is employed, a hard soap results, potash, on the other 
hand, yielding a soft soap. For the separation of the 
soap from the glycerine advantage is taken of the fact 
that although soap is soluble in water, it is not soluble 
in a solution of common salt. The boiling of the fat 
with caustic soda is therefore followed up by throwing 
a quantity of salt into the boiler ; the soap separates, 
rises to the top, and is removed to iron moulds. 

Although the chemistry of soap-making was not 
understood until about a hundred years ago, the art 
has been practised for many centuries. At the present 
time, soap-making is one of the leading chemical 
industries, and this country is ahead of all others both 
in regard to scientific methods of production and amount 
turned out of the factories. We not only make most 
of our own soap, but send over i?l, 000,000 worth 
annually to other countries. 

The candle and soap industries have this in common, 

246 



FATS AND OILS 

that they both use fats ;b their raw material, and turn 
out glycerine as a by-product Until the lad quarter 
of a century, however, comparatively little attention 
was paid to thi> latter material; the soap-maker, indeed, 
simply ran the spenl liquors containing the glycerine, 

" lve>,*" as they are called, into the nearest water-COUrse. 

Nowadays, because of its use in the manufacture of 
nitro-glycerine for dynamite and frlagjing gelatin, glycerine 
has become a valuable product, and successful efforts 

have been made to recover it from the spenl liquors 

of the soap-works. This utilisation of what was formerly 
run to waste has, of course, cheapened the production of 

BOap. Indirectly, therefore, the discovery and manufac- 
ture of nitro-glycerine and the explosives into which 
this dangerous substance enters may be regarded as 

pro m oting cleaning 

It has been stated On good authority that the flourish- 
ing condition of the soap industry in this country has 
: chiefly due to the profits arising from the recovery 
the glycerine In any case, there is no doubt that 
the utilisation of waste products is very often of the 

greate-t importance to the industry concerned. More 

than that, the history of by-products is a mbjed erf 
the mosl fascinating interest even to the general reader, 
and eequenl chapter wil] accordingly be devoted 






CHAPTER XXII 

HOW MAN COMPETES WITH NATURE 

EVERY one has doubtless observed that in the grow- 
ing infant the bump of destructiveness is early 
developed, and that it is only at a later stage that 
this impulse to take things in pieces is succeeded by the 
desire to put together — to construct. In the gradual de- 
velopment of the science of chemistry we can detect similar 
stages. In one of these the energies of chemical workers 
were mainly directed to breaking down all the various 
substances found in nature, and discovering the simplest 
elements of which matter consists. At another and later 
stage attention has been chiefly directed to building up 
from simpler materials the various products of the 
earth. 

We might, in fact, speak of the one method of work as 
destructive and of the other as constructive. Such de- 
structive work, or analysis, as the chemist calls it, has, 
however, served a very useful purpose ; it was necessary 
to demolish the fantastic structures of the alchemists, and 
to get down to the bed-rock of fact, before a building 
could be reared worthy of the name of science. Once the 
foundation was well and truly laid, the constructive work 
of building — synthesis, as the chemist calls it — could be 
taken in hand. 

Why, the reader may ask, should we trouble ourselves 
to build up substances which Nature readily supplies ? 

248 






HOW MAN COMPETES WITH NATURE 

Why not accept her gifts gratefully, and cease worrying 
about " synthesis 

Now in at least one case which has already been men- 
tioned, the reply to these questions is quite simple The 
value of nitrate of soda as a nitrogenous manure has been 
emphasised, and at present the beds of this material in 
Chili are largely requisitioned for the purpose. Bui this is 
here Nature's stores are limited, and the prosped 
that in thirty or forty years the supply from this BOUTOe 

will come to an end has stimulated the discovery of some 

>\(>i\ o( utilising the vast stock of nitrogen in the 

osphere. The way in which this is being effected 

has already been described, and it is sufficient to point 

out that the artificial production of nitrate, regarded 

W attempt to imitate Nature, has a very practical 

obj< 

However it may be now, there i- no doubt that in the 
rtagi g of synthetic chemistry, tin- work was under- 

:i and carried out purely in a spirit of scientific in- 

ion, without any reference to utility and without 

the ion of favours to come, in the shape of hard 

•urn-. Innumerable chemists have spent their 

in unremitting toil, striving only to let the light 

ire corner; their labours may have led 

rs to application- of great commercial value, 

hut all that these early pioneers bad was the love of their 

work, the honour and the glory ! Nowaday- the coin- 

of chemistry ; much in evidence, and 

i» in many ca-es a Decenary part of the 
ory — it- brains, in ! it ion and research 

out with the definite obged of making monej i- i 

littl. ■ nantic than heroic attempts to win Nat' 

of Itnov ilone, hut the farmer i> 



HOW MAN COMPETES WITH NATURE 

more immediately practical, and we must recognise that it 
has been very productive in results. 

Synthetic chemistry may be said to date from a certain 
red-letter day in 1828, when Wohler succeeded in pro- 
ducing carbamide (urea) artificially. This bald statement 
does not sound very stirring, but Wohler's achievement 
was big with meaning for the years to come. It must be 
admitted that if the general reader were to listen to the 
long tale of Wohlers discoveries, he would probably not 
select the artificial production of carbamide as the most 
useful or the most interesting. A boy would be interested 
in Wohler as the first who described the curious behaviour 
of mercury thiocyanate, which swells up into a worm-like 
shape when heated — a scene familiar to all who have looked 
at " Pharaoh's Serpent.' 1 But Wohler's fame does not 
rest on the discovery of Pharaoh's Serpent, or even on 
the preparation of aluminium, which he was the first to 
accomplish, but mainly on the production of carbamide 
from inorganic materials. 

Now carbamide is essentially an animal product. The 
cast-off nitrogen of the human body is thrown out in the 
form of carbamide, and the average adult produces about 
1 ounce of this substance every day. It is got rid of in 
the urine, which contains 1 to 2 per cent, of carbamide in 
the dissolved condition. 

At the time of Wohler's discovery the view was every- 
where held that the complex substances occurring in plants 
and animals were produced only by the action of a special 
vital force ; it was therefore vain to hope that these 
products of the organism— organic substances, as they 
were called — could possibly be obtained from the dry bones 
of inorganic material. Wohler's success in producing 
carbamide in the laboratory from purely inorganic sub- 

250 



HOW MAN COMPETES WITH NATURE 

stances gave ■ severe blow to these old ideas; in fact, it 

■t them altogether. "Vital force * was evidently nol 

as ary lor the production of organic substances — a 

conclusion which has been abundantly confirmed since 

Wohler's time, and i*> being daily confirmed in every 

chemical laboratory. 

Suppose, now, we try to till in the details of this epoch- 
making discovery, and to Bee how by mere laboratory 
ations it is possible to build up or synthesise carba- 
mide from its elements. The inorganic substance which 

ifl most nearly related to carbamide is a compound of 

carbon, hydrogen, oxygen, and nitrogen called ammonium 
ate, and Wohler discovered thai by merely evaporat- 
ing to dryness a solution of this compound in water a 
large proportion of it was changed straighl away into 

carbamide. If. then, we show that ammonium cyanate 
can lx- made from its constituent elements in the labora- 
tory, w. istified in Baying that carbamide can be 

duced artificially. 

The first link in the chain between the separate (lenient-, 

boo, hydrogen, oxygen, and nitrogen at (he one end, 

and ammonium cyanate a( th< other, ifl acetyl* nc. We 

een thai this gas can be produced from 

inn?. rials; by heating lime and carbon in the 

calcium carbide is produced, and to gel 

ram calcium carbide only water is required. 

But a more direct synthesis of acetylene is possible by 

making an elec boo rods in an atmOS- 

re of hydrogen; under these conditions acetylene, 

which i- a com; bon and hydrogen, i- produced 

in -mall quantity. 

V gas, when mixed with nil md 

with 



HOW MAN COMPETES WITH NATURE 



the latter element, forming prussic acid, or hydrocyanic 
acid, as the chemist calls it ; and when prussic acid is 
neutralised with potash we obtain the salt potassium 
cyanide, a very poisonous compound of potassium, carbon, 
and nitrogen. Potassium cyanide can be very easily 
melted in an iron dish, and in the molten state readily 
absorbs oxygen from the air, forming a salt called potas- 
sium cyanate, a compound of potassium, carbon, nitrogen, 
and oxygen. If this substance is dissolved in water and 
sulphate of ammonia added, we get a double exchange 
taking place, whereby ammonium cyanate and potassium 
sulphate are formed. 

This gradual building up of carbamide may be repre- 
sented graphically in the following manner : — 

Carbon Hydrogen Nitrogen Potash Oxygen Ammonium sulphate 



1 1 








1 

Acetylene 

i 


i 

Prussic acid 
1 




Potassiui 


n cyanide 

i 




i 

Potassiun 

i 


i cyanate 






Ammc 
C 


. 1 
miuni cyanate 

4 

irbamide 



It may be objected that besides the four elements, 
carbon, hydrogen, oxygen, and nitrogen, three compounds 
have been introduced into this synthesis, namely, potash, 
water, and ammonium sulphate. If space and the reader's 
patience permitted, it might, however, be shown that 
these compounds also can be built up out of their con- 
stituent elements, so that the whole chain is complete, 

252 



HOW MAX COMPETES WITH NATURE 
i the simple carbon, hydrogen, oxygen, and nitrogen 

to the organic compound carbamide. 

Wdhler's wonderful discovery was interesting not only 

Wise carbamide was the first Organic compound to be 
prepared in the laboratory from inorganic materials, but 

also because it consists of the same elements as are presenl 

in ammonium cyanate, and, more than that, the carbon, 
hydrogen, oxygen, and nitrogen are presenl in exactly the 
same proportions in the two compounds. The extra- 
ordinary tact that two chemical compounds which are 
quite distinct in external appearance and behaviour may 
contain the same elements united in the same proportions 
was very pooling to chemists at that time, although 
nowadays it is taken quite as a matter of course. Later 
workers haw shown that such differences are due to a 
subtle distinction in the way in which the atoms 
are d in the molecules : the internal anatomy of 

tin- molecule is different in the two eases. 

Since that red-letter day in 1828 synthetic chemistry 

has made gigantic strides, and we have learned to produce 
artificially hundreds of naturally occurring products, in 

many cases SUcfa an imitation of Nature has very little 

res! tor anybody outside of a chemical laboratory, 

but, on the Other hand, the synthetic product docs 
occasionally come into the market AS a competitor of 

the natural substance. An interesting example of this 

rniahed by the history of aliirin. 

•hi- valuable dye-stuff was obtained from 
the maddi ar root, and large areas of Prance, Holland, 
Italy, and Turk< cwnef to the growth of the 

.t. cloth dyed with alizarin has been found on 

I in mumi I that it- ire goes back to a lvmote 

age. Yet within the diort -pace of forty jmn this 



HOW MAN COMPETES WITH NATURE 

ancient product of the vegetable world has been un- 
ceremoniously hustled out of the market by the artificial 
dye. The latter can now be produced more cheaply than 
the natural alizarin, with the result that the cultivation 
of the madder plant has almost ceased. 

The magnitude of the trade revolution thus due to the 
synthetic production of a natural dye may be gauged 
from the fact that for ten years previous to the discovery 
the value of the annual import of madder into Great 
Britain averaged i?l ,000,000, while ten years later the 
value had sunk to .£24,000. All this meant unem- 
ployment and privation to the people engaged in the cul- 
tivation of the madder plant, but indeed it is frequently 
the case that the advance of science, although beneficial 
to society as a whole, involves suffering to many individuals. 

In explaining the synthesis of carbamide we were at 
pains to follow the successive steps by which it is possible 
to build up the final compound from the component 
elements. It must not be supposed, however, that the 
manufacturer of alizarin starts with the elements of which 
that substance is composed. As a matter of fact, the 
chief raw material of alizarin is anthracene, a hydrocarbon 
which is extracted from coal tar. It has been shown that 
this hydrocarbon can be synthesised in the laboratory, and 
as everything else used in the manufacture of alizarin can 
be similarly built up from inorganic materials, it follows 
that we have here an instance of the artificial formation 
of a complex natural product. The manufacturer, how- 
ever, who has to consider the price of raw material and 
the cost of labour, starts with some other natural pro- 
duct, in this case anthracene, which is at once cheap and 
easily obtained. 

Natural alizarin has gone down before the artificial 

254 



HOW MAN COMPETES WITH NATURE 

product, and a similar fate seems to be in store for 
another well-known dye-stuff, namely, indigo. It is some 
time now since chemists managed to produce indigo 

synthetically in the laboratory, but, as is frequently 
found, it is quite a different thing to turn out products 
profitably on the manufacturing scale. Dividends become 
a prime consideration, and the question arises whether the 
artificial product can be manufactured cheaply enough to 
Compete successfully with the natural article. In the 
of indigo the interval of time between the laboratory 
Synthesis and the successful manufacture on a large scale 
was considerable Years elapsed before all difficulties 
nie, but Science prevailed in the end and the 
artificial production of indigo on commercial line- i- an 

ompliahed fact. 

The law materials on which the manufacture of indigo 
depend- art- (1) the hydrocarbon naphthalene; ('2) am- 
monia, both obtained from coal : (8) acetic acid, obtained 
from wood; (J.) oxygen, from the air. Starting with 
these, chemists have elaborated a process whereby artificial 

indigo is turned out sufficiently cheaply to compete with 
the natural dye-stuff. Already the latter has been hard 
hit. and the cultivation of the plant from which it is 
obtained is apparently doomed. Hie value of the indigo 

orted from India m >70,000 in 1895, and only 

I 1904, while of the total quantity of indigo 
nmed in the various countries of the world at the 
- lit time between 80 and 90 per cent, i- the artificial 

This latter, it must be clearly understood, is 
not a mere substitute; it is exactly the same chemical 
compound as is derived from the plant. 

The synthesis of indigo on a manufacturing scale i-> 
indeed one of tip- mo I remarkable achii rementi of modern 



HOW MAN COMPETES WITH NATURE 

chemistry. It has been spoken of as "a monumental 
example of scientific skill, patience, and resourcefulness," 
and as " absolutely unparalleled in the recent history of 
chemical industry." 

The reader will perceive that the advance of chemical 
science, while it is to the interests of the community as a 
whole, may involve serious trouble, and possibly extinction, 
to special industries. There is no partiality in the busi- 
ness. At one time it is France's turn to suffer from 
artificial alizarin, then India feels the competition of 
synthetic indigo ; now it looks as if Japan and China 
were to find out in a similar way what the advance of 
science may mean in connection with camphor. 

True Japanese camphor is obtained from a tree which 
belongs to the laurel family, and which is native to China 
and Japan. The wood is cut into small pieces and 
subjected to the action of steam, whereby the volatile 
camphor is carried off and condensed in a cool vessel. 
The amount of this crude camphor annually exported 
from China and Japan has in recent years run to about 
3000 tons. Most of the camphor supplied from these 
sources is employed in the manufacture of celluloid, but 
a certain quantity is used up in medicinal preparations 
and in explosives. 

An enormous amount of labour has been expended in 
the study of the chemical nature of camphor, and this has 
at last borne fruit in the synthetic production of the 
substance. The starting-point is turpentine — a resinous 
liquid which exudes from various trees belonging to the 
pine family. When turpentine is boiled, a liquid known 
as " oil of turpentine " distils over, and from this liquid 
camphor is produced by laboratory processes into which 
we cannot enter here. Synthetic camphor is identical 

256 



HOW MAN COMPETES WITH NATURE 

with natural camphor in all ordinary physical and 
chemical properties, and provided that a plentiful supply 
of turpentine at a moderate price is available, the next 
few years may witness a repetition of what has already 

aired in the cases o\' alizarin and indigo. 

It is a very confuting circumstance that there is also 
on the market a product known as "artificial camphor,"' 
which, indeed, has an odour resembling that of true 
camphor, but which is chemically quite a different sub- 
stance. Synthetic camphor, on the other hand, is chemi- 
cally identical with the natural product. 

Another and quite different direction in which we have 
; trying with success to imitate Nature is in the 
manufacture of rubies. In an earlier part of this volume 
it was stated that ftfoissan had been able to produce real 
diamond^, BO small, however, as to be of no ornamental 
value. The specimens commonly known as "artificial 
diamonds" are spurious; the "paste* 1 used in their 
manufacture i» chemically quite different from the dia- 
mond, which, as the reader knows, is simply crystallised 
Artificial rubies, however, are chemically identi- 
cal with the natural gems, and are indistinguishable from 
them. 

Rubies and sapphires are practically pure alumina in 
the crystallised condition; they consisl almost entirely 

of this compound of aluminium and oxygen. Alumina 

itself is a colourless substance, and the colours of the 
natural ston due to the pit m ikv of small quantities 

of the oxides of chromium and iron. If the crystallised 
alumina i^ free from these other materials, we have the 
mineral known as corundum, which in hardness is second 

Oldy to the diamond, and with which, in an impure form, 

- i t h.t tin oseftd and the 

i 



HOW MAN COMPETES WITH NATURE 

ornamental, in the shape of emery and ruby, are very 
closely related. 

The artificial production of rubies depends simply on 
the careful fusion of alumina at a high temperature, 
and the addition of a small quantity of dichromate of 
potash to produce the colour. Great care must be taken 
in the cooling of the fused alumina ; if allowed to solidify 
and cool very rapidly, it is in an unstable condition, like 
glass which has been similarly treated. It is therefore 
annealed, by putting the artificial ruby while still at a 
high temperature in a bed of silver sand, so that the 
cooling takes place very slowly. 

Sapphires may be made in a similar fashion, except 
that the colouring material added is oxide of cobalt in- 
stead of potassium dichromate. The artificial production 
of sapphires, however, has not been so successful as that 
of rubies. 

A new and very striking way of making these gems 
has been tried lately. It has been found that when 
natural colourless crystals of corundum — white sapphires, 
as they are called — are exposed to the action of radium 
bromide, they undergo a gradual change of colour. Some 
specimens assume a blue tint, others a pink, and others 
still a brownish orange ; so that stones of any desired 
tint may be obtained. 

In these and many other ways, then, man has been 
trying, and is trying, to imitate and compete with Nature. 
When we look back to that day in 1828 when the 
artificial production of carbamide was first accomplished, 
we are filled with wonder at the marvellous advance 
which has been made in the interval. Not only have 
we learned how to obtain artificially numbers of valuable 
natural products, but we can turn out of our laboratories 

258 



HOW MAN COMPETES WITH NATURE 
and factories many useful chemical compounds which, 

BO tar Bfl ire know, do not OCCUI in Nat hit at all. We 

must, however, beware erf pride, We musl confess that, 

although we can produce organic compounds in the 

laboratory, we cannot turn out an organism. That 
is a different thing altogether, and there is no prosped 

that the breath of life will ever be evolved from any 

chemical mixture, however cunningly devised 






CHAPTER XXIII 

THE ADULTERATION OF FOOD 

THE chemist's imitation of Nature, as shown in the 
previous chapter, has led to results of marvellous 
interest and practical value, but in some cases, 
unfortunately, the imitation practised at the present 
time has an unworthy object. Just as there are some 
individuals who devote their chemical knowledge to the 
manufacture of bombs and infernal machines, so there 
are others who engage in the objectionable practice of 
adulterating food. 

There have always been knaves ready to defraud the 
public, and the adulteration of food is no new thing. 
We have evidence on record that in past centuries bread, 
wine, butter, and drugs were all liable to adulteration. 
Things are bad enough now, but if one were to judge 
from a certain booklet published in the beginning of last 
century, the old days were even worse. This striking 
pamphlet has for part of its title — " Deadly Adulteration 
and Slow Poisoning, and Death in the Pot and the 
Bottle ; in which the blood-empoisoning and life-destroy- 
ing adulterations of wines, spirits, beers, bread, flour, tea, 
sugar, spices, cheesemongery, pastry, confectionery, medi- 
cines, &c, are laid open to the public," and the author 
expresses himself occasionally in the gloomiest terms 
regarding the state of matters in his day. u Bread," he 
says, " turns out to be a crutch to help us onward to 

260 



THE ADULTERATION OF FOOD 

the grave, in-trad of being the staff of life. In porter 

there is do support, in cordials no consolation, in almost 

ything poison, and in scarcely any medicine cure.* 

The adulterations practised at thai time, however, 

comparatively crude, and with present-day methods 

and instruments they would be easily detected. As a 

result of the advance of chemical knowledge and practice, 

the adulterator has been forced to refine his nefarious 

methods, so thai at the present time many of the alien 

substances introduced into our food can be delected only 

by the skilled analyst. "For ways thai are dark, and 

trick- thai are vain/" the modern adulterator would indeed 
be hard to beat. 

We must, of course, allow that it" we call every foreign 

addition to our food an adulteration, there are c 
when* the offence is not very heinous. As examples of 

objectionable additions, we may take the 

curing and flavouring of butter. Butter fat itself in 

the natural state has generally nothing like the yellow 

rur which we are accustomed to see in the commercial 

article, and the explanation is that in the greal majority 

uses an artificial colouring matter, quite harmless in 

d introduced. This is done, it is said, 

becmw the public prefers to have a highly coloured art icle. 

Again, the dill n flavour of various sampL 

butter is not natural : it i> induced by the presence of 

tin micro-organisms which are cultivated for the 
purpose. Tliese adulterations, although undesirable, are 

not harmful, and may !><• regarded as mildly fraudulent 

on with others which are commonly practi 

M iiimn fo tain foreign materials intro- 

ith the dired objed of defrauding tin- public 

profil to the idler. Even the 
261 



THE ADULTERATION OF FOOD 

ordinary food-stuffs of the breakfast-table are not always 
what they seem, with the exception, perhaps, of sugar, on 
the purity of which one can depend. The reader may be 
interested to hear a little about the ways in which these 
foods are adulterated, and about the methods by which 
the fraud can be detected. 

In the case of milk the chief, and one might almost 
say the natural, adulterant is water. New milk contains 
as much as 87 per cent, of water, and the uninitiated 
might suppose that it would be very easy to add a little 
more without detection. Careful analysis, however, will 
always reveal any such manipulation, although it must 
be borne in mind that there may be a certain difference 
in the richness of milk from various cows. 

One method which the chemist has at his disposal is the 
determination of the specific gravity — that is, he finds out 
how much heavier the milk is than an equal bulk of 
water. It is worth while remembering that the first 
recorded determination of the specific gravity of a sub- 
stance was in connection with a question of fraud. Hiero, 
the King of Syracuse, had commissioned a goldsmith to 
make him a crown out of a certain quantity of gold. 
When the smith brought the finished crown, Hiero some- 
how suspected that there was an admixture of base metal, 
and asked Archimedes to find out for him whether this 
was so. The philosopher took a lump of pure gold equal 
in weight to the crown, and put each into a vessel full 
of water. He found that more water overflowed from 
the vessel into which the crown had been put than from 
the other, and concluded rightly that the crown must 
contain some lighter and baser metal. So the deter- 
mination of specific gravity as a means of detecting fraud 
is a time-honoured practice. 

262 



! 



I THE ADULTERATION OF FOOD 
It' a bulk of water were taken which weighed exactly 
ounces, an equal bulk of pure new milk would weigh 

about 103 ounce-, a little le— or a little more, according 

to it- source. That is, the average specific gravity of 

milk maybe taken a- 1*0). It', then, a certain sample of 
milk had a specific gravity of only 1*02, we might be 

-ure that it had been "watered. m On the other hand, 
the fact that the specific gravity of a -ample i- 1*03, 
d<>e> not prove the milk to be satisfactory; for, curiously 
enough, it i- possible, by a judicious combination of 
ring and skimming, to get a product which has the 
-ame specific gravity a- the original milk. 

The reader, of course, know- that the fat contained in 
the milk — in other word-, the cream — rises -lowly to the 
surface ; but he may not have drawn the conclusion that 
this fat must therefore be lighter than the milk. What 
removing the cream — that IS, the -kimmed 
milk — i- actually heavier, bulk for bulk, than the fresh 
milk: il- specific gravity is higher than 1*08, By adding 

i to this -kimmed milk in the proper proportion, the 

specific gravity i- brought down to the normal figure 

d this "milk"* i- indistinguishable from fresh 

milk unless further te-t- are applied. 

It will probably be suggested that a mere glance at 
this " milk " would -how that it had been -kimmed and 

Hut our adulterator i- not ily caught ; 

he p fraud upon fraud, exhibiting an ingenuity 

which i- worthy A ludiciou- admixture 

dye to skimmed and watered milk i- found 

to I my app . and the public il 

1 with its milk supply. So is the adulterator ; 

Ifl -old hi- kk milk " at the md he has 

still tl il to dis] 



THE ADULTERATION OF FOOD 

Since, then, the appearance of the milk and even the 
determination of its specific gravity may fail to give any 
proof of adulteration, further examination is necessary. 
The analyst must proceed to find also what is the amount 
of fat present in the milk. This is very quickly ascer- 
tained by treating a measured quantity in a centrifugal 
machine ; the fat or cream under these circumstances 
separates almost immediately, and its bulk may be deter- 
mined. If the amount of fat is less than 3 per cent., the 
milk has certainly been tampered with, since the normal 
product never contains a smaller percentage of fat than 
this. A thorough examination would include also the 
determination of the non-fatty solids, consisting chiefly of 
casein and milk-sugar ; but a description of this would 
take us rather far. 

Butter is another household article that is readily and 
frequently adulterated, although the recent Butter and 
Margarine Act should do something to protect the public. 
The usual frauds practised in the case of butter are 
(1) the sale of " renovated " or " process " butter as fresh 
butter, and (2) the substitution of a certain amount of 
cheap beef fat or lard for the true butter fat. Reno- 
vated butter is obtained from rancid butter by a pro- 
cess in which the objectionable matter is removed ; the 
product is rendered sweet for the time being, and is sold 
as choice butter. 

Artificial butter, on the other hand, or margarine, 
as it is commonly called, is prepared from beef fat or 
lard, which is worked up with ordinary butter and 
colouring matter so as to resemble the real article. 
Besides a certain difference in the taste of butter and 
margarine, there is one very simple method, known as the 
spoon test, by which they may be distinguished. If a 

264 " 



THE ADULTERATION OF FOOD 

little genuine butter is melted in a large ipoon over a 
small Bunseu flame, and the heating is continued, t ho 
butter ultimately boils quietly and bams up to the edge 
of the spoon. Margarine, treated in the same way, 

splutters about and crackles, hut does not foam. Hie 

* selling margarine under the name of pure 
butter is probably dying out, but it is not m> very long 
oe a l>old individual was prosecuted for actually ad- 
ding a pn tor the "scientific" blending of 

butter with beef tat or lard. Science, it would seem, 

covers a multitude of sins. 

A food-stuff which i- very frequently adulterated i> 
chocolate. This substance is obtained bv grinding cocoa 
nib-, which are the crushed kernels of cocoa beans. The 
nibs consist to about 1~> per cent of a fab the so-called 

cocoa butter, and in ihi- resped are quite different from 

shells of the cocoa bean, which contain only 'I to 3 

the fat. Seeing that the price of cocoa nibs 

I tin times that of cocoa shells, the common 

practice of adulterating chocolate with powdered cocoa 
Us i- distinctly profitable This fraud is best de- 

• d by th»- aid of the miCTOSCOpe, an instrument which 
SSary equipmenl of an analytical 

t*s laboratory. To tin- practised eye the presence 
of t d shells is at once obvious. 

is another adulterant of chocolate or cocoa which 

d with the aid of the microscope, and that 

h. This substance i- very widely distributed in 

the plant Mi- in all SOTts of vegetables 

I ' h obtained from these 

. sucfa a- wheat, rice, | , and m 

are chemically when the] lined 

und< o^copi . the granules of which fh< \ 



THE ADULTERATION OF FOOD 

are found to be surprisingly different in shape and size. 
The granules of wheat starch are circular, those of potato 
starch are oval, while those of rice starch are many-sided ; 
the granules from maize starch, as found, for example, in 
cornflour, are also many-sided, but are uniformly much 
larger than rice-starch granules. It is therefore possible 
for a skilled analyst to determine with the microscope 
whether any starch, and, if so, what kind of starch, has 
been used in adulterating a given food-stuff*. He can 
also discover at once whether a certain kind of starch is 
pure or is contaminated with another kind. Obviously 
there is a temptation for the adulterator to add a cheap 
starch to a more expensive one, say potato starch to 
arrowroot, keeping the price the same. The microscope, 
however, soon exposes such a fraud. 

Substances which in some cases are to be regarded as 
regular adulterants are those used as preservatives. It is 
now generally agreed that a dairyman who knows his 
business does not require to add preservatives such as 
boric acid and formaldehyde, even in the hottest weather. 
Moreover, the passage of these substances into the 
digestive organs is not to edification. The amount of 
formaldehyde which must be added to milk in order 
to preserve it is certainly exceedingly small — 1 part in 
10,000 of milk will keep the latter sweet for five or six 
days — but it must be remembered that in the case of 
children who consume considerable quantities of milk, the 
total amount of preservative taken into the system be- 
comes appreciable. 

Similar objection may be taken to the employment of 
boric (or boracic) acid. This is used as a preservative of 
milk less frequently than formaldehyde, and it is generally 
mixed with borax, its sodium salt. Boric acid, by the 

266 



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O o 

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TX 



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THE ADULTERATION OF FOOD 



I we use tor preservative and other purposi ! comes 
i Tuscany, where numbers of steam jeta of volcanic 

)ffio?iii a.s they are called -- arc to be found 
fagning from the ground. This steam contain- small 
quantities of boric acid, and when a tank to hold water 
h built round the blowhole, the boric acid is condensed. 

gradually accumulates in the water of the tank, and is 
then obtained by evaporation, the steam jets themselves 

being used to promote the process. Successful resull i 
en obtained also from artificial Bofflom^ -tailed by 

ring into the lower strata. 

re other chemicals which are often used as food 
uch as -all, sugar, and vinegar. These 
themselves foods to some extent, and they 
are tin. ■ much less objectionable than purely anti- 

five- like boric acid and formaldehyde, 
common salt (-odium chloride) in preserving 
tter and meat is well known to every one. and if is not 

regarded as an adulterant. A curious effect is produced 

olution in which heel' is salted contain- some 

itrate of potash) as well as sodium chloride. 

The saltpeti es the meal to prese r ve it- natural red 

• Mir. which would be destroyed, partially, at least, by 

the action of common -alt alone. 

1 gg form of food which is fortunately out 

cb of the adulterator. Ai leasl he cannot 

imitate the egg as a whole, and his turn comes only 

en the question of an egg substitute arises. In this 

line be ha- displayed hi- u-« od brought 

ui all the ni- 
gra 1 •_:-. hut which uninatioa are found 

hoit of that itandaid. In one I 

i 



THE ADULTERATION OF FOOD 

on record it was stated with a great show of authority 
that the composition of a certain egg substitute was 
" based on the scientific analysis of natural eggs," which, 
it should be noted, contain a fair proportion of nitro- 
genous matter. When tested, the product in question 
was found to be entirely innocent of nitrogen, and con- 
sisted of nearly pure tapioca starch with a little common 
salt and colouring matter added. This is another ex- 
ample of the way in which the name of science is 
taken in vain. 






268 



CHAPTER XXIV 
THE \ AM E OF THE BY-PRODUCT 

IT is perhaps difficult tor the outsider to realise that 
the manufacture of useful and valuable materials, 
which has been rendered possible only by the advance 
of chemical science, but which we now take m> much 
as a matter of course, has meant at the same time the 
oduction of enormous quantities of rubbish The 
iterial which Nature supplies may contain only 
mall proportion of the substance we wish to 
it ; the rest is s () much refuse, and, unless we 
devise some way of using it, has to go on the dust- 
w brad the gold, and the dross is left 
Now rubbish-heaps there will be as long as the world 
lasts, bul provided thai they are not a public nuisance, 
they are kept out of our sight, we accepl 

them as a necessary evil. It will be readily admitted, 

however, that a rubbish-heap which as late as 1888 

150 teres oi ground, and was then receiving 

i a trifling daily addition of 1000 tons, is no ordinary 

ati This heap of alkali waste, about which we 

i\ later on, was at the same time 

a public : ; the neighbourhood was, and .still 

.jectionable odour. 

in which the u;eic pro- 
duct chemical industry, although lesi obooxioui 
than alkali waste, accumulate at to alt<< cm- 



THE VALUE OF THE BY-PRODUCT 

manageable rate, and it is no wonder that manufac- 
turers and their chemists have made heroic attempts 
to deal with this rubbish problem. Indeed, the story 
of the way in which the attacking forces have slowly 
advanced, at great expenditure of energy, patience, and 
fortune, reads like a romance. 

The reader, however, will readily understand that 
besides the mere wish to avoid the awkward accumula- 
tion of rubbish, the desire to make something out of 
it has helped in the solution of the problem. The 
manufacturer is only too pleased if the chemist can 
tell him how waste material can be converted into a 
useful by-product. Indeed, history shows that the dis- 
covery of methods for utilising the waste products of 
a chemical industry has frequently saved it from going 
down in the face of fierce competition. Economy demands 
some utilisation of the waste material, and this has been 
effected with much profit to the manufacturer even in 
industries where there is no particular difficulty in getting 
rid of it. 

An instance of the production of much waste material 
is to be found in the brewing industry. The main 
object of brewing is, of course, to get beer, but during 
the process of manufacture a very large quantity of 
carbon dioxide is produced. The alcohol in the beer 
is obtained by the fermentation of sugar, in which process 
sugar is changed into alcohol + carbon dioxide. The 
quantity by weight of the carbon dioxide formed during 
the fermentation is almost equal to that of the alcohol, 
and the process is generally carried on in open vessels, 
so that the gas simply escapes into the air, and is lost. 
Carbon dioxide, that is to say, is a waste product of 
the brewing industry. 

270 



THE VALUE OF THE BY-PRODUCT 

It is quite easy to cany out the fermentation in 

closed vessels provided only with an outlet for the 

on dioxide and by this method the gas could be 

collected and condensed to the liquid form in steel 

bottles; in this shape carbon dioxide IS a marketable 
commodity. Such a conversion of the chief waste pro- 
duct of the brewing industry into a useful by-product 

hai actually been carried out, and the carbon dioxide 
so obtained has found application in refrigeration and 
in the preparation Of aerated waters. Nowadays, how- 
. the attempt to recover the carbon dioxide as a 
by-product is very seldom made, because, from the com- 
mercial point of view, it is not worth while. 

A waste product which is more tangible but less efl 
to deal with than carbon dioxide is blast -furna< 

From what was said in a previous chapter, the reader 
will understand that iron-smelting consist- essentially 

in heating together crude iron oxide, carbon in the 
form of coke, and a Mux, such as lime, to remove the 

ny material from the ore in a tluid form. At the 

end of the operation two things are obtained, namely, 

1 -lag, the latter being simply the Mux + 

the earthy material from the iron ore. It is run out 

be blast fornaoe in a molten condition and is a sort 

of cross bet we. and cinder-. Tin- unpromising 

berial is turned out in Great Britain at the rate <>f 

nearly twenty million ton- annually, and the mere re- 
moval of tin- from the foundry involves the 

Miielter- in 'Ollsiderable eXp In -oiin 

it i- taken out and -hot into the mau of the all J. 

-ea. In other cases, as in the Black Country, 

it i- allowed to accumulate in huge, unsightly DflOUnd 

— veritable rubbish-h ipc i rn civilisation* 



THE VALUE OF THE BY-PRODUCT 

It is perhaps too much to hope that such an enormous 
mass of waste material will ever be entirely devoted to 
useful ends instead of disfiguring the landscape and 
covering up the fertile soil, but recent work has un- 
doubtedly led to encouraging results in the utilisation 
of slag. Much of it is employed in road-making and 
in reclaiming waste land, but in addition there is now 
made a very large quantity of slag cement, for which 
purpose the finely powdered slag is mixed with lime. 
Another purpose to which considerable quantities of 
slag are devoted is the making of "slag wool.*" This 
curious product is somewhat similar to "glass wool," 
the name in each case indicating a resemblance to cotton 
wool. When a jet of steam is directed against molten 
slag, little globules of the liquid material are blown off, 
each with a long, thin tail or filament. By mechanical 
means the filaments are separated from the globules, 
and slag wool consists simply of masses of the filaments. 
It is a non-conducting, non-inflammable material, and 
as such is usefully employed in covering steam-pipes 
and boilers. In virtue also of its non-conducting pro- 
perties, it is used to coat refrigerating plant. 

It is very curious that while there has been such 
difficulty in utilising blast-furnace slag, there is another 
kind of slag, turned out from steelworks, which has 
found a ready application. If the reader considers for 
a moment how this basic slag, as it is called, is obtained, 
he will understand why it is a more valuable by-product 
than blast-furnace slag. 

Steel is obtained by blowing air into molten pig-iron ; 
the impurities in the latter are thereby oxidised, and 
the purified metal is then supplied with the requisite 
quantity of carbon to convert it into steel. It is par- 

272 



THE VALUE OF THE BY-PRODUCT 

ticularly important to get all the phosphorus removed 
from the metal, and tlii-- u best Becused by adding 
quicklime to the molten pig. Any phosphorus which 
i> p re s en t in the latter is oxidised by the Masi of air, 

and ifl then in B condition to combine with the lime. 
The slag, therefore, which is obtained at the end of 
the operation, contains phosphate of lime, and it ifl 

just the presence o( this phosphate which makes basic 
luaMe a- a fertiliser. The greater parti Bay 
1 ,500, 000 tons, of the basic dag which is turned out 
of the steelworks of Europe u Bold for this purpose. 
The only thing n e c e ss ar y in order thai its fertilising 
1 1 should be available is that it be finely ground. 
This is quite a straightforward operation, m> that we 

have here an excellent example of the way in which 

the waste material of an industry i^ converted very 

simply into a valuable by-product. 

More striking than any of the caaeo yet quoted ifl 

the tale of the soda industry in Great Britain. Not 

once, but twice during its history, a waste product of 
the mosl di ble description ha- become a valuable 

rce of income to the manufacturer. Refuse ha- been 

into riches, and one of the by-products has 

• the most important part of the out put. 

I la is found in nature to n limited 

extent, but it is the artificial production which alone 

of any importance, Hiii bach to about the 

time of tin 1 h Revolution, when a certain Prench- 

i, Leblanc by name, firsl showed how to turn common 

irbonafc Any one who Beeki to 

prcx: la on a large scale is bound to star! with 

. it i- the iid of < m 1 i 1 1 1 1 1 <»f which there 

' plentiful BUpply in N The piore- 



THE VALUE OF THE BY-PRODUCT 

which Leblanc devised laid the foundation of an enormous 
industry, and "has given us cheap soap and cheap glass ; 
but he himself, poor man, did not have much joy out 
of his invention. The unsettled nature of his time 
prevented his getting any profits ; he did not even 
receive the reward promised by his own Government, 
and at length, in disappointment and despair, he put 
an end to his own life. 

Leblanc's process for the manufacture of soda has been 
worked in England for about ninety years, and in order 
to appreciate its strange and chequered history, we must 
understand what the process is. The first stage is the 
conversion of common salt (chloride of soda) into sulphate 
of soda, or " salt cake," as it is called, by heating with 
sulphuric acid. This operation results, not only in the 
formation of salt cake, but also in the evolution of 
torrents of hydrochloric acid gas. While the industry 
was in its infancy the hydrochloric acid had little or 
no value, and was allowed to go up the chimneys and 
pollute the air. The results of this were remarkable ; 
the vegetation in the neighbourhood of the alkali works 
was devastated ; the smell pervading the atmosphere 
was noxious, and articles made of iron, such as locks, 
gutters, and tools, were rapidly corroded. No wonder 
that the alkali works were unpopular institutions. 

The manufacturers thought that by building very high 
chimneys, up to 500 feet, the acid gas would get dis- 
sipated in the upper layers of the atmosphere, but this 
plan did not work out in practice, for the fumes descended 
like a pall on still wider areas, and the vegetation vanished. 
A striking commentary on the anxiety there was about 
1840 to get rid of this public nuisance is furnished by 
the patent which was taken out for a sort of floating 

274 



THE VALUE OF THE BY-PRODUCT 

■dt cake furnace. Weather permitting, the furnace 
praa to be towed out to sea, and there allowed to do 
its wont, 90 tar as pollution of the atmosphere was 
concerned 

Gradually, as time wenl on, another method of dealing 
with the waste hydrochloric acid came into vogue. This 
easily soluble in water, bo that by making 
it pa-- through a chimney or tower packed with coke 
over which water was constantly running, it was possible 
he greater part of the acid fumes. This was 
undoubtedly the righl direction in which to go to work, 
but the absorption of the acid was never complete, and 
the number of alkali works increased very rapidly, 
the public nuisance caused by the uncondensed acid 
vapours aras d as ever. It is estimated thai even 

ite as 1860 the English alkali works were pouring 
out aboul a thousand ton- of this corrosive hydrochloric 
• tv week. Besides, those manufacturers who 
ibsorbing it were left with enormous quantities 
uid liquor on their hand-. There was not much 
ind for this; it had little value, and the bulk of it 
accordingly tipped into the nearest stream. Here 
the aeid did fresh damage, for it lulled all the fish ; the 
pie immediately tied with tin* stream objected 

to its pollution, and complaints were rerj numerous. 
Altogether rather an awkward situation for the alkali 
Vet within tin- 
tin- arho of affiu altered Hie hydro- 
chloi . which had been such an unmitigated nuisance 
fhody since the itarl of the alkali industry, 
ed to \h- a valuable product Hie alkali manu- 
fact' • ful to keep and use every 
the mb whkh i b fore be 



THE VALUE OF THE BY-PRODUCT 

would have given anything to be rid of. In fact, the 
utilisation of the hydrochloric acid rapidly became the 
most profitable part of the manufacture of soda by 
Leblanc's method. 

What was responsible for this sudden transformation, 
for this striking conversion of waste into wealth ? One of 
the chief factors was undoubtedly the removal of the duty 
on paper in 1861, as the reader will agree when the 
connection between these apparently unconnected events 
is explained. 

The removal of the restricting duty gave an immense 
stimulus to the demand for paper materials. Cotton and 
linen rags, which had previously served for the manu- 
facture of paper, were no longer adequate to supply the 
demand. Other raw materials, straw, wood, and esparto 
grass, were therefore requisitioned, but these substances 
had to undergo very drastic treatment before they 
appeared in the form of paper. Among other things, 
they required much bleaching, and the source of bleaching 
materials is hydrochloric acid. Chlorine, prepared from 
hydrochloric acid, is used for the purpose, either directly 
or after conversion into bleaching powder. The connec- 
tion between the paper duty and the fortunes of the soda 
industry is therefore pretty obvious. 

The discovery of this valuable outlet for their hydro- 
chloric acid, and the passing of the Alkali Act in 1863, 
stimulated the manufacturers to devise improved methods 
of absorbing the acid ; and so efficient is the absorption 
now that the escaping gases tontain less than 0'2 grain of 
hydrochloric acid per cubic foot. Any one who allows a 
larger proportion of the acid to escape is liable to a fine. 

Having seen the good fortune which at length attended 
the efforts of the alkali trade to get rid of waste product, 

276 



THE VALUE OF THE BY-PRODUCT 

migfal suppose thai there would be contentment all 
round, among the public as well as among the manufac- 
turer* But this was not so, and the cause of trouble 
and stage of the Leblanc soda proo 
\\ i have been bo occupied in following up the history 
of the waste hydrochloric acid that we have yei to lean 
fate of the sail cake which is produced at the same 
time. In the second A the Leblanc process the 

salt cake IS mixed with limestone and eoal dust, and 

heated in a furnace. The chemical changes which take 
place in this furnace are somewhat complicated, but the 
net result is a product known as "Mack ash," consisting 
chiefly of carbonate of soda and sulphide of lime With 
the help of water, the soda is extracted from the black 
■sh, the portion which is insoluble being termed "alkali 
This objectionable refuse contain- both the 

urn from the limestone and the sulphur originally 

i in the manufacture n\' the sulphuric acid for the 
Hrst stage. Of these, the sulphur is especially valuable, 
but far many lo n no satisfactory method could be 

led \"i recovering it from the waste, which was simply 
thrown away. 

I lmulation of this waste material in the neigh- 

bourhood of alkali works led to much unpleasant! 

•] when it was -tamped down and 1 over with 

a la] moisture and sir gradually u r(, t at the 

with the result that sulphuretted hydrogen gas 

was given off into the atiiHwphfrft Apart from the 

abominable - CUmula) thrm- 

. and their magnitude b such thai ippn- 

tportanoe of t • industry from a mere 

glan bese rubbish-heaps. Those in the neighbour- 

hood ol Widm . to which in 



THE VALUE OF THE BY-PRODUCT 

the beginning of the chapter, are estimated to contain 
8,000,000 tons of material. 

To the trouble which this waste brought upon the 
manufacturers of soda by Leblanc's method there was 
added the menace of serious competition. The ammonia- 
soda process, as it is called, has during the last thirty- 
years become a formidable rival of the Leblanc process, 
and at the present day considerably more than half the 
world's production of soda is made by the newer method. 
Curiously enough, while the Leblanc process was a French 
patent which has been worked mostly in England, the 
ammonia-soda process was an English patent which com- 
mended itself first and foremost to the Germans. This 
later method of manufacturing soda has many advantages, 
and although we cannot go into details, we may mention 
that brine pumped directly from the salt beds is converted 
into soda in such a way that the product is a purer one 
than that yielded by the Leblanc method, and that there 
are no disagreeable waste products. 

The reader might suppose that the ammonia-soda 
process, with all these advantages, would speedily displace 
the older Leblanc process. But the latter has offered 
a stubborn resistance, a fact attributable to the once 
despised and obnoxious hydrochloric acid. The value of 
this by-product has kept the Leblanc process going. At 
the same time everybody concerned realised that, with 
this serious competition to face, all must be done to 
effect economies, and, if possible, recover that lost sulphur 
from the alkali waste. As one of the leading chemical 
manufacturers in this country said in 1881: "The 
recovery of sulphur from alkali waste, as a means of 
cheapening the cost of production by Leblanc's process, 
has become of vital importance.' 1 

278 




; * 



THE VALUE OF THE BY-PRODUCT 

At length, after a series of abortive attempts, suco 
attained Bya process patented in England in 1888, 
90 per cent of the sulphur in alkali waste is recovered, 
and can be sold as pure sulphur. Even in 1898, only 
five years after the patenl was taken out, 85,000 tons of 
sulphur were recovered by this method in England alone. 
Prom the public point of view also, tin's utilisation of 
alkali waste is welcome, far sulphur was the constituent 
he waste which was responsible for its objectionable 
pro] Once the sulphur is removed, as is done 

nowaday-, the residue is innoenons and unobjectionable, 
ba1 the nose of the community is do longer offended 
v have private profit and public interest been 

ther as in this utilisation of alkali waste. 
With the economy thus effected, the LeManc proo 
has on a new lease of lite. At the same time it 

i- interesting to note thai some manufacturers who use 
the LeManc process turn out no carbonate of soda at all, 
but soda, bleaching powder, and pure sulphur. 

It i- in secondary products that the 

i advantage over its rival 
itory of the toda industry is interesting because of 
ping fortune, and because of the illustration it 
famishes of the value of the by-product Even vet it is 
not qui! in that the industry is at the end of its 

. tor the manufacture <>t" alkali and bleach by 
methods is being rapidly developed^and bids 
formidable competitor. Time only can dhow 
methods wSl be able to overthrow the 

oldei processes manufaetu 






CHAPTER XXV 

VALUABLE SUBSTANCES FROM UNLIKELY 
SOURCES 

THE last chapter will have shown the reader how 
waste products, sometimes merely embarrassing in 
their character, sometimes definitely obnoxious, can 
be brought to play their part in our industrial economy. 
We are encouraged to believe that everything has its 
place, could we but find it out, and that the waste material 
of our industries is frequently wealth in disguise. Perhaps 
in no case has the disguise been more complete than in 
the by-products of gas manufacture. Some reference has 
already been made to these in chapter xiii., but the 
lessons of the alkali trade may be suitably enforced by 
a study of the marvellous story of coal tar, and other 
equally unsavoury products of the gasworks. Here also 
science has shown how useful and beautiful substances can 
be obtained from the most unpromising material, and 
how so-called waste products can be made to contribute 
largely to revenue. 

The reader may remember that in the dry distillation 
of coal four products are primarily obtained, namely, coke, 
ammoniacal liquor, tar, and coal gas. Little more need 
be said about the coke and the gas except to point out 
again that even the sulphuretted hydrogen in the latter, 
which must be removed on account of its harmful character, 
is made to pay part of the cost of production. The 

280 



VALUABLE SUBSTANCES 

amount of sulphur in coal ifl very -mall, only 1 to % 

quivaleni to an average of about 36 lbs, per 

ton. Only about one-third of this amount reaches the 

purifiers as sulphuretted hydrogen, and yet so large 

is the quantity of coal which is treated in the gasworks 

Grieai Britain that in the aggregate the recovered 

Sulphur amounts to thousands of tons pel annum. In 

j Lsworks tin's recovered sulphur is used in the pre- 
paration of sulphuric acid, which in its turn is employed 
in fixing ammonia and forming ammonium sulphate 

Besides the sulphuretted hydrogen, then 1 is another im- 
purity in crude coal gas which has to be removed, and 
which at the same time i^ made to contribute to the cost of 

luction. This is the poisonous compound of hydrogen, 
•on, and nitrogen known as hydrocyanic acid. By Wlit- 

■ mica! methods it is extracted from the crude 
converted into potassium ferrocyanide, a substance 

which i^ perl ter know n as yellow prussjate of potash. 

a this product it is easy to prepare either Prussian 

. for the manufacture of printing-ink, or potassium 

Tin's latter compound is extensively employed 

ion and in electro-plating. Thus it i- that 

the enable impurity present in the crude coal 

)i less than 1 part in 1000 i> converted 

:cts. 

\ otb valuable by-product ol manufacture i- 

snip ammonia, obtained bom the ammonia 

liquor* Tin- amount of nitrogen in coal is 1 to I 

rit only a pari of this i- obtained in the form 
of ammonia. R<mgfr1y ipeaking, pre may ^*»y that 

■il put into th. '•' Ihs. 

of ammonium snip] I from the li«|uor. 

In I Britain the annual output of •on :;<>in 



VALUABLE SUBSTANCES 



the gasworks alone in the form of ammonium sulphate 
is enormous — about 160,000 tons. It is valued as a 
nitrogenous manure, and large quantities of it are exported 
to Germany and other countries for this purpose. 

The remaining primary by-product of coal-gas manu- 
facture is tar, the unlovely qualities of which need no 
exposition. Yet out of this dirty, sticky substance the 
chemist has been able to evolve all manner of useful and 
wonderful things, as we shall see presently. To begin 
with, we may note that the tar helps to pay the cost of 
producing coal gas, as is shown by the following table. 
This gives approximately the amounts of the various 
charges incurred in manufacturing 1000 cubic feet of coal 
gas, as well as the prices which the by-products or 
residuals will fetch. 

Cost of 1000 Cubic Feet of Gas 



2 cwts. coal at lis. 6d. per ton 
Purification . 
Salaries . 
Wages . 
Maintenance . 

Total . 



s. 


d. 


1 


If 





0J 





o| 





2i 





H 



1 81 



Returns from Residuals of 2 cwts. Coal 



Coke . 
Tar, 1 gallon 
Ammonia products 

Total . 



s. 






d. 
6 

4 



o 91 



The net cost, therefore, of making 1000 cubic feet of gas 
in the holder is about lid. 

282 



VALUABLE SUBSTANCES 

The share borne by the residuals in defraying the ootA 
of making coal gas baa an important bearing on the 

•ion of gas vermu electricity far lighting purpo 
No doubi electricity has replaced gas to a considerable 

nt, hut apart from the fact that gas IS now largely 

employed far beating, the constant discovery of new uses 
for the by-products of gas manufacture tends bo cheapen 

the cost of production. 

SP long after the introduction of coal ^;b the tar was 

a nuisance, a disagreeable by-produd the removal of which 
involved the manufacturer in considerable expense. The 

demand for it was exceedingly small and far short of the 
ititv which was turned out of the gasworks. Two 
men who carried on the distillation of tar in these early 
day- have hft it on record that the gas company gave 
them the tar on condition that they removed it at their 
own expense. The volatile spirit or "naphtha/' which 

got by distilling tar, was employed by 
Mi-. Mackintosh of Glasgow in dissolving indiarubber for 

the manufacture of the waterproof material which b 
his nan 

In 1 Sijs a patent was taken out for impregnating or 

wood with heavy oil from coal tar, and this 
ed an important outlet for the £a^ mannfactin 

Wood that has to 1)« d to the action of 

Of to a moist -oil will la-t much longer if i' ifl 

in this ep oil; and for the treatment of 

rail- ipfa poles, and wooden beams tor 

tensively osi d even at tin- 

present day. 

• r, which was distilled out of 

the \\ was i pickling timber tl 

a very limited outlet. Bom ued for dissolving 



VALUABLE SUBSTANCES 

indiarubber or making varnish, and some was employed 
for illuminating purposes. A patent flare lamp for the 
combustion of this naphtha was invented sixty years ago, 
and is still part of the regular equipment of a coster's 
barrow. 

The thorough utilisation of coal tar was not possible 
until chemists had made a complete study of its con- 
stituents. This was carried out to a large extent by the 
middle of last century, and one result of these investi- 
gations was to demonstrate the presence in coal tar of 
the following important compounds : — benzene, toluene, 
phenol or carbolic acid, naphthalene, and anthracene. 
All of these, except phenol, are compounds of carbon and 
hydrogen, that is, hydrocarbons, and their importance 
arises from the fact that they are the starting-points for 
the manufacture of the aniline dyes and other synthetic 
products of that kind. The actual proportion of these 
five compounds in coal tar is not great — as a rule, perhaps 
less than 12 per cent., but they are the constituents 
which chiefly concern us here. 

They are extracted from coal tar by the process of 
distillation. Some are much more volatile than others, 
and when the tar is boiled these distil over first, are con- 
densed, and so are separated from the less volatile con- 
stituents. The temperature of the tar in the boiler is 
continuously raised, and the process of separating a more 
volatile from a less volatile part is repeated. 

In this way the tar distiller obtains a number of 
portions or " fractions," and has finally left in his boiler 
a quantity of pitch, amounting to about 60 per cent. 
of the original tar. The various fractions in which 
the distillate is collected are known as "first runnings," 
" light oil," " carbolic oil," " creosote oil," and " anthra- 

284 



VALUABLE SUBSTANCES 

oil." When each of these is farther subjected to 

fractional distillation, the important compounds already 

mentioned are obtained in a state of comparative purity. 

All thi> clever sifting out of the constituents of coal 

tar was very interesting from the purely scientific point 

. and though that alone would never have made 

coal tar the highly important commercial product that 
it is to-day, still we must admit that the present realised 
value of coal tar goes hack ultimately to those purely 
scientific researches carried on about the middle of last 
:ry. It is well to realise how much of our modern 
comfort and luxury is traceable to such researches, for 

there i^ sometimes a disposition on the part of the coin- 
oft* at anything which cannot he shown 
to have an immediate nse. This fa a narrow view of 
the acquisition of knowledge. The history of the last 

ttury teaches us most emphatically that the 
advance of a chemical industry is secured not by the 
employment of practical men only, hut by the co- 
operation of these With the skilled chemist. The appar- 
ently unpractical researches of the latter art-, with tin- 
aid of the engi] Averted into practical manufactur- 

w ( i eat Britain have been don to 

app: the value of the trained chemist and the 

research laboratory ; the result is thai we have sufli 
in certain industries where these I uv essential to 

\ •• H i- an Englishman who mad* the d; 
which the whole coal-tar indu-try is founded III 

1856, th 9 William IVrkin. while -till a lad of 

1 that when aniline was oxidised by 
!i. a beautiful purple colouring mal 

which we i ik of M i i A 



VALUABLE SUBSTANCES 

demand soon arose for this, the first artificial dye, and 
Perkin, with the assistance of his father and brother, 
started a small factory for its production at Greenford, 
near London. 

The importance of Perkin's discovery in relation to 
the utilisation of tar lies in this, that although aniline, 
the raw material for the manufacture of mauve and other 
dyes, occurs only in traces in coal tar, it is very easily 
produced from benzene, which, as we have seen, is one 
of the regular constituents. For this purpose benzene is 
first treated with nitric acid, which converts it into 
nitro-benzene — a substance which in smell closely resembles 
oil of bitter almonds, and which is used in scenting soaps. 
Nitro-benzene, when treated with iron filings and hydro- 
chloric acid, is converted into aniline. This liquid is 
a basic substance, which contains the elements carbon, 
hydrogen, and nitrogen, and unites readily with acids to 
form salts. Perkin's discovery, therefore, that aniline 
was the parent substance of artificial colouring matters 
meant that there was a new outlet for the benzene from 
coal tar. 

Mauve was only the first of a long series of artificial 
dyes which chemists have succeeded in building up out 
of the constituents of coal tar. Some of these, such as 
alizarin and indigo, have competed successfully with the 
naturally occurring dye, while others, so far as we know, 
do not occur in Nature at all, but are of purely laboratory 
origin, such as magenta and Bismarck brown. 

The phenomenal growth of the artificial colour industry 
can best be realised by contrasting the modest works 
at Greenford, where Perkin began the manufacture of 
mauve, with the extensive dye-works of Germany at the 
present time. The manufacture of artificial colouring 

286 






VALUABLE SUBSTANCES 

matters has there attained the rank of a distinctively 

national industry, and the annual value i)\' the dyes 

orted to other countries is about £8,000,000. It 
somewhal bitter reflection thai the foundation of 

this huge industry was laid in England, and that it 

flourished here for about twenty years after its start, 
only to dwindle subsequently to unworthy proportions, 
The truth is that the German manufacturer; recognised 
the value of the scientifically trained man, in this industry 
above all others; they spenl large sums on Laboratorj 
ligations, in the confidence that these would ulti- 

• ly bear fruit, and their faith has had its reward. 
Wo Id thai our English manufacturers had had a little 

this virtue ! 
The importance of the coal tar products in the modern 
ately emphasised by the celebration of the 
I rar Jubilee in L906. After the lapse of fiftj \« 
iiists, manufacturers, and dyers from all parts of the 

world met in London to honour Sir William lYrkin, the 

he industry. The chief meel u laid in 

the Boyal Institution, where in L8S6 another English 
chemist, I discov e red beniene, tin- hydrocarbon 

which, one might say, has been al tin- bottom of the whole 

in*---. ()n tin- table at which distinguished men of 

industr} offered their i ilations to Bir 

Will:. . !'• I i small bottle of bensene, the iden- 

en which Paradaj had prepared eight • 
bef i 

Tin- M ho!. ! ho a the aniline and ot 1m 1 d\ • - h i\ e 

in unin\ it in^ in 
| is realK bus : it i- truly, a -omr < 

W( must n 1 1 1 * 1 1 i 1 that coal 

ie prodi 



VALUABLE SUBSTANCES 

besides colouring matters. Even Punch at one time 
felt moved to wonder at the host of things that have their 
origin in coal tar, and delivered himself of the following 
lines : — 

" There's hardly a thing that a man can name 
Of use or beauty in life's small game 
But you can extract in alembic or jar 
From the ' physical basis ' of black coal tar. 
Oil and ointment, and wax and wine, 
And the lovely colours called aniline ; 
You can make anything from a salve to a star, 
If you only know how, from black coal tar." 

"Anything from a salve to a star" is rather a big 
order, but the variety of purposes to which the derivatives 
of coal tar are applied is certainly very remarkable. In 
photographic developers, in the colour of microscopic 
sections, in patent fuel, in the colour of our butter, in 
artificial perfumes, in the surgeon's antiseptics, in the 
latest shade of tie, and in the explosive lyddite, we may 
detect the trail of the tar. 

Some readers may be interested to know that among 
the drugs to which the study of benzene and its deriva- 
tives have led are the well-known antipyrine and phena- 
cetine, as well as a host of others which would not be so 
familiar. Whoever wan J ;s a local anaesthetic, a hypnotic, 
or an antiseptic can have his requirements met by some- 
thing which has been derived from coal tar. 

As a last example of the unexpected things that have 
cropped up during the study of coal tar products we may 
take saccharine. This substance is prepared from the 
hydrocarbon toluene, and therefore indirectly from coal 
tar. Its most remarkable property is its sweetening power, 

288 



VALUABLE SUBSTANCES 

which i^ said to be three hundred times as great as thai of 
r. This being so, it might be looked oo aa a formidable 
com; . l)ut doubts have arisen as to its Buita- 

hilit ) od, and its sale is now restricted by law in ei 

Euro] : it can be purchased i\\ the druggists 

-, hut not at th r*a It is valuable to people 

irho suffer from diabetes, and who have therefore to avoid 
the use of su 

Enough has been said in this chapter to convince the 

ler that very valuable substances can be obtained from 

the most unlikely sources. It" he is an optimist, ttiese 

uill help to confirm him in his vien of lite. If he is 

a pessimist, prone I the unlovelj side of things, he 

s m U b that th , tut v even in coal I 









CHAPTER XXVI 
CHEMISTRY AND ELECTRICITY 

"T F the reader has had the patience to accompany us 
I thus far, he will have learned that chemistry, so far 
from being an isolated system of facts, is intimately 
related to many other departments of scientific activity. 
The chemist has something to tell us about agriculture, 
about the composition of the stars, about the relation of 
animals and plants to the atmosphere, about the physio- 
logy of nutrition, and other diverse matters. Especially 
when one considers the modern applications of science to 
industry and manufactures, does the all-pervading influence 
of chemistry become apparent, for in the most unexpected 
quarters chemical changes are utilised and made to con- 
tribute to the requirements and comforts of life. 

It is not surprising to find that the bearing of chemistry 
on other branches of science has led to the development 
of special study on the borderland of chemistry. Hence 
it comes that there is nowadays such specialisation as is in- 
dicated by the names "Agricultural Chemistry," "Physical 
Chemistry," and "Biochemistry." Another lateral branch 
of the science with a double-barrelled name is " Electro- 
chemistry," a subject which is of vast importance at the 
present time, not only from the point of view of the pure 
scientist, but also from that of the man who is mainly 
interested in applied science. 

The relation between chemistry and electricity is one 

290 



CHEMISTRY AND ELECTRICITY 



of mutual indebtedness. It is a long time now since 
Volta first showed ho* chemical forces might be utilised 
in the production of an electric current -how chemical 
might be converted into electrical energy. The 
chemical cell which Volta constructed consisted merely 
of a plate of copper (C) and a plate of sine (Z) immersed 
in water to which a little sulphuric acid had been added 
Volta found that it' the two plates 
ined by a wire outside the 
liquid, then an electric current 
pantrd through the wire. 

The electric current obtained 
uch a cell i> not manu- 
factured out of nothing: there 
i (ju'td pre qua While the 
cell i- running and producing cur- 
bing 
irhich mean a lowering of the 
-tore df energy in the cell. \ 
been pointed out by the 
author of "Tin- Romance of Modern Electricity,* this 

tly analogous to what happen- in th< of I 

"grandfather's clock. "' The store of energy in the clock- 
depends on the height to which 
they have been wound by muscular force, and the driving 
Itwork for any given time fa possible onlj 

the cost > i!in(!i of the en esiding in the 

rhts ; they will !>♦• lour)- down at the Hid of the 

d than th- at the beginon 

Similarly arrant out of a chemical oeU 

in so : _res go on wbkh l<< 

ivaflablx j in the celL The nature 

iges which may thui !><• utilised in the p 

/ 




no. 12.— Yolta'i Cell. 



CHEMISTRY AND ELECTRICITY 



duction of an electric current are very well illustrated 
by reference to the Daniell cell, which is only slightly 
different from Volta's original one. The metals in the 
Daniell cell are the same as those in Volta's cell, zinc 
and copper, but instead of being immersed in acidulated 
water, the zinc plate dips in a solution of sulphate of 
zinc, and the copper plate in a solution of sulphate of 

copper. The two solu- 
tions are prevented from 
mixing by a partition of 
porous earthenware, gene- 
rally in the form of a 
cylindrical pot, inside 
which is the zinc sulphate 
and the zinc pole of the 
cell, and round which is 
the sulphate of copper 
solution with the copper 
pole. In the form of 
Daniell cell represented in 
the diagram the copper 
pole is replaced by a 
copper pot which holds the copper sulphate solution. 

If, now, the zinc pole is connected with the copper pole 
by means of a wire, an electric current runs through this 
wire from the copper to the zinc. The passing of a 
current is evidence that work is being done by the cell, 
and the question therefore arises — What is the source 
of the energy ? 

In the grandfather's clock the equivalent for the driving 
of the works is found in the gradual fall of the weights 
— a fairly obvious phenomenon ; but a cursory inspection 
of the Daniell cell does not reveal any marked change 

292 




Fig. 13.— Daniell Cell. 



CHEMISTRY AND ELECTRICITY 

which might tx Led as responsible for the electric 

current. Closer examination, howev e r, shows thai the 

current has been obtained only al the expense of certain 

alterations in the cell. If, before allowing the cell to 
run, say tor an hour, we wen to weigh the two poles, 
then, on weighing them again afterwards, we should find 

that the zinc pole had become lighter, and the cop 
pole heavier. Further, we should find thai the solution 
round the zinc pole contained more sulphate ol 
than at the -tart, and that the solution in contad 

with the copper pole had Lost some of its copper 

sulphate. The change-, then, which occur during the 

iuction of the current are (1) the disappearance of 

some of the zinc to form zinc sulphate, and (.2) the 

of copper on the other pole from the copper 

sulphate. All this mighl be represented very simply 
in the following way: zinc + coppcr sulphate-»copper 

+ zinc sulphate, the arrow indicating that the sub- 
stances on the left are replaced by the substances named 
on the right 

Tlii- may strike the reader a- something quite novel, 
but as a matter of fact a chemical change of exactly the 

same kind ha- already been considered in earlier chapters. 

thing which, a- was painted out, served to support 
the alchemists 1 belief in the transmutation of metals 
the rion than when a clean steel knife-blade has 

dipped is lution of copper sulphate it look 

:t it had b tttO copper. Tliih_ 

i. and careful invesl 

Hon ha- dioun (I) that the formation of Copper i- only 
d. and (2) thai in Inch 

m the l- ain quantity 

solution a- sulphab I 



CHEMISTRY AND ELECTRICITY 

change might in fact be represented as follows : iron + 
copper sulphate -f copper + iron sulphate. 

Now something exactly similar happens when a piece 
of zinc is employed instead of the knife-blade. If we 
were to put a few bits of zinc foil in a solution of copper 
sulphate, and leave them for some time, we should find 
that they had entirely disappeared, and that in their 
place a spongy mass of metallic copper lay at the bottom 
of the solution. This simple little experiment shows 
that the change zinc + copper sulphate->copper + zinc 
sulphate is one which takes place spontaneously. 

A little reflection will convince the reader that the 
forces which bring about any spontaneous natural change 
can, if properly harnessed, be made to do work of various 
kinds. The force of gravitation, under the influence 
of which an unsupported body falls to the ground, is 
harnessed for the service of man in innumerable ways, 
as, for instance, in the grandfather's clock. The con- 
version of quicklime + water into slaked lime is a 
change which takes place spontaneously, and, as we 
have se£n in an earlier chapter, is accompanied by a 
considerable increase in bulk. The force of this ex- 
pansion has occasionally been utilised in blasting coal, 
by the simple device of packing quicklime into a hole 
in the coal and moistening it with water. The chemical 
forces set to work immediately, and the mechanical 
force of the expansion which accompanies the reaction 
suffices to split the coal apart. 

The Daniell cell is another illustration of this same 
general principle. It is simply a device whereby the 
spontaneous chemical change zinc + copper sulphate 
-» copper + zinc sulphate is harnessed and made to 
do work. The chemical energy of the cell is con- 

294 



CHEMISTRY AND ELECTRICITY 

verted into electrical energy, as evidenced by the pro- 
duction of an electric current. 

Besides the reaction which has jusl been discussed) 
there arc many others which have been similarly harnessed. 
Among the better known electrical cells, which, like 
the Daniel] cell, arc devices for transforming the enei 

1 chemical reaction into electrical energy, arc the 
Grove cell, the bichromate cell, ami the Leclanchd cell. 

Another very common form in which chemical enei 
1, ready for conversion into electrical energy, i> 
the secondary cell or accumulator, sometimes called a 

storage cell. This IS a sort of artificial chemical cell, 

and when complete consists of two lead plates immersed 
in dilute sulphuric acid, i^wc of the plates, however, being 

ially prepared and coated with peroxide of lead. 

In this condition the cell is a store of chemical energy, 
and when the plates <>r pole- are connected by a wire, 
a current passes through the latter from the peroxide 

plate to the lead plate If much currenl is taken out 

of the secondary cell, H gets run down, like the weights 
in * indfather's clock, hut like these it can be 

"wound up"" again. Tin- is done by passing through 
the oil. say from a dynamo, a current of electricity 

in the Opposite direction to thai of the eurreiif which 

the cell itself yields. The result of thi- i- to put into 

cell ,-i fresh upply of electrical energy, which is 

idv f>r immediate i 
I been said, it will be plain tl 

tnistry has marl.- some very importanl contributions 
to the development and application of electricity. This 

. has b plj repaid, and i 

who lopmenl of chemistry will 

« hich 



CHEMISTRY AND ELECTRICITY 

plays in the chemical world. As was said at the be- 
ginning of the chapter, the relationship between chemistry 
and electricity is one of mutual indebtedness. 

We have seen how chemical changes have been utilised 
in the production of electrical energy ; suppose we glance 
now at one or two of the ways in which electricity has 
contributed to the advance of chemical knowledge and 
practice. It will be found that some of the most recent 
achievements of industrial chemistry have been rendered 
possible only by the co-operation of the chemist and 
the electrical engineer. 

It must be remembered that in some cases the electric 
current has been used only indirectly in order to bring 
about chemical changes. It is a familiar fact, illustrated 
by the common electric glow lamp, that the passage 
of a current through any body produces heat. The 
greater the opposition offered by the body to the passage 
of the electricity, the more intense is the heat gener- 
ated by a given current. If, therefore, we employ very 
powerful currents, and pass them through bodies which 
offer a stout resistance, an enormous amount of heat 
is generated, and a very high temperature is reached, 
much higher, in fact, than is attainable by any ordinary 
methods. Many substances which are usually quite in- 
different to each other, react readily at such high tempera- 
tures, so that the electric current, merely by its heating 
action, has been extremely useful in extending the 
chemist's field of knowledge. Some of the interesting 
facts which have thus been discovered at the high 
temperature of the electric furnace have already been 
described in chapter xvii. 

It is, however, not only by virtue of its heating effect 
that the electric current has been of service to the 

296 






CHEMISTRY AND ELECTRICITY 

►verer and manufacturer. II has a re- 
markable power of splitting op compounds into ampler 
bs, provided it i^> applied to these compounds while 
they are either in the dissolved or the molten con- 
dition. The value of the electric current for this pur] 

demonstrated by the famous English chemist, Sir 
Humphry Davy, who succeeded in showing thai potash 
and *oda, which up to the time df his experim< 
had been regarded as elements, \ illy compounds. 

It was by passing an electric current through fused 
rtic potash thai Davy firsl obtained potassium, a 
tal which is v to interact with air and moisture 

that it - 1 only under naphtha. Potassium 

v of hard hut ter, and il may easily 

be cut with a knife; the clean, fresh surface of the 
I by cutting is quite shiny, but it rapidly 
}\i action of air and moisture. 
When a small piece of potassium is thrown into wat 
hyd isb are imm< diately gener- 

ated, and the heal of the reaction is w intense that 
m< - fire. The pouring on of p 
►re, a process which is usually associated with the 
•nction of fire, may in some actually lead to 

Sodium, th< metal which Sir 

aphry Davy fi] the 

at, is very similar to potassium) 

hut 
'1 1 

! I I ime 

Rnglitth i . Michael Faraday, 

the laws which this pb o. I le 

i WO w i: d with the pol 

d* or in 






CHEMISTRY AND ELECTRICITY 

the fused salt itself, decomposition took place, with the 
result that the metallic part of the salt was liberated at 
one wire (the cathode), and the acidic part of the salt at 
the other wire (the anode). Investigation, indeed, has 
shown that the passage of an electric current through 
a salt solution consists in a general movement of the 
metallic part towards the cathode, and a general move- 
ment of the acidic part in the opposite direction ; but 
most obvious to the onlooker is what happens at the 
wires or electrodes. 

What the observer sees taking place at the electrodes is 
sometimes only the secondary, not the direct, result of 
electrolysis. For instance, if we were to pass a current 
through a solution of common salt, or sodium chloride, 
to give it the systematical chemical name, the metallic 
part of the salt, the sodium, would be liberated primarily 
at the cathode. Any particle of sodium, however, which 
was thus liberated, would immediately be set upon by 
the surrounding water molecules ; hydrogen gas would be 
evolved, and caustic soda would be formed in solution 
round the cathode. The action of water on sodium 
prevents our obtaining this metal by the electrolysis of an 
aqueous solution of any sodium salt. 

Sometimes the wire or plate which forms the anode is 
attacked and dissolved by the acidic part of the salt which 
is being electrolysed. An interesting example of this 
is furnished by the electrolysis of a solution of copper 
sulphate between copper electrodes. During this process 
the metallic part of the salt, the copper, is deposited on 
the cathode, which therefore becomes gradually heavier. 
The sulphate, or acidic part of the salt, instead of being 
liberated at the copper anode, attacks it, forming copper 
sulphate, which dissolves in the water. So the net 

298 



CHEMISTRY AND ELECTRICITY 

result of the electrolysis is thai copper is transferred from 

the anode to the cathode, the latter increasing in freight 

is the farmer becomes light* 

His simple operation is really of very great technical 

importance, tor the greater pari of the world's supply erf 
per is refined on the same principle Plates of the 
impure copper which conn- from the -inciter are used s 
anode- in bath- of acidified copper sulphate, while sh 

of pure copper act BS the cathodes. When a current 

is passed through such a bath, the anode is gradually 

•bed, as already desc ri bed, and pure copper i- d< - 
ported on the cathode. He impurities in the anode 
either pass into the solution and remain th 
settle down to the bottom of the bath as a soil of slud 

The small quantities of gold and silver which are present 
in crude copper are thus deposited in the du hicfa 

is worked up for the sake of these valuable metal- after 

the elect roly-i- i^ o\ 

It i^ estimated that in the Tinted Stale- alone about 
ton- of copper are refined every year by this 
electrolytic pre 57,000,000 ounce- of silvn 

(l,)() ounces of gold being obtained as by-prod 
from the dudg 

El . i- applied, 1 1 c > t only in the 

purification tals which have been produced by 

Iting, but in obtaining the metals themsdvi 

their compound-. Aluminium fuillishei the h nple 

owadayi it i- obtained exclusively 
by rtrolysu of alumina, the oxide of the a* 

iriOQS form- and U 

arth, but if it i- to 

iminium, it 
must first be purified and OOQ the dro v which 



CHEMISTRY AND ELECTRICITY 

accompanies it in the natural state. The mineral which 
is used in this country as a source of alumina is 
"bauxite," obtainable in large quantities in the south- 
east of France. 

When pure alumina has been prepared from bauxite it 
is dissolved in a bath of molten cryolite — a Greenland 
mineral — and subjected to the decomposing action of an 
electric current. Electrolysis takes place quietly at a 
temperature of about 1500° Fahrenheit, with the result 
that the aluminium from the alumina is separated at the 
cathode, and the oxygen goes to the anode. The latter 
is made of carbon, and at the comparatively high tem- 
perature which prevails, it combines with the oxygen 
from the alumina, and passes away as gaseous carbon 
monoxide. The metal, on the other hand, collects at 
the bottom of the bath in the molten condition, and is 
run off from time to time. 

There are some very interesting points about the 
production of aluminium in this country. As already 
stated, the raw materials of the industry, the bauxite and 
the cryolite, are obtained from France and Greenland 
respectively ; the bauxite is purified in Ireland (where also, 
by the way, this mineral is to be found), while the actual 
production of the metal is carried on in some of the most 
outlying parts of Great Britain. We usually associate 
metallurgical processes, such as tin- and iron-smelting, 
with busy centres of population, and it may seem strange 
that in order to find aluminium works we must go to the 
remote Scottish Highlands. For this curious circum- 
stance, however, there is a very sufficient explanation. 

Even the non-technical reader will perceive that in 
order to produce aluminium cheaply, it is absolutely 
necessary to have inexpensive power for the dynamos 

300 




A Striking ] 

'. m of aluminium water po» 
^n to the f.i 

tTZC £ " down for thi* purpovr at Kinloch> 

each of which is thirty-nine inches 
a qua- 



lei 



CHEMISTRY ANT) ELECTRICITY 

which yield the electric current. Now the cheapest way 

Iriving a dynamo is to utilise water-power. This can 

be done on the large BCale only where there is a big 
waterfall, or where there is an adequate reservoir, con- 
stantly replenished from natural source-. 

tar as this Country is concerned, these conditions are 

dised in the Highlands of Scotland, and hence it 

tefl that the aluminium industry is located at Fo\ 

in Inverness-shire, and at Kinlochleven, on the borden sf 
j 11 shire and Inverness-shire, The water of the reservoir 

ted at the latter place i- carried in a conduit to a 
point near the factory and about !)00 feel above it ; from 
this point the water is run down to the turbines in pipe* 
i diamel 
Oiu rientific forefathers, could they see it, would 
regard this new feature of the land-cape with much 
curiosity: they would not understand what water-pipe- 

could possibly have to do with the aluminium industry. 

Perhaps, also, when the ptesenl of scientific devdop- 

passed away, our far-off descendants will 

the ruins of these outlying in- 

. much as we to-day endeaxour to 

the riddle of Druidic al and Roman remain . 






CHAPTER XXVII 
SOME INTERESTING FACTS ABOUT SOLUTIONS 

IF the reader were to glance at the titles of the papers 
published in any modern chemical journal, he would 
probably be struck by a number of the most un- 
pronounceable and incomprehensible names. It is perhaps 
a little difficult for him to realise how any one can 
profitably spend time working at "The Reduction of 
Hydroxylaminohydroumbelluloneoxime " or " The Pre- 
paration of Ethyl-a-cyano-y-keto-y-phenyl-butyrate," but 
science is now so specialised that many of the advance 
workers are necessarily engaged in fields which seem very 
remote from everyday concerns. Not only, however, is 
new and strange ground constantly being broken ; the old 
problems, which earlier workers thought they had settled, 
are regularly coming up for review ; new facts are daily 
discovered which bear on these problems, and which, if 
they do not clear up difficulties entirely, at least con- 
tribute to their settlement. 

So it has been in recent years with the problem of 
solutions ; the last two decades have witnessed an extra- 
ordinary activity on the part of chemists anxious to 
throw light on such questions as : What happens to 
sugar and common salt when they are dissolved in water ? 
How is the behaviour of the water affected by their 
presence ? 

These may at first sight appear to be questions of 

302 



FACTS ABOUT SOLUTIONS 

pmely academic interest, but they really have a direct 

bearing on many practical problems. To lake one 

: a knowledge of the properties of solutions fa 

itial to any one who attempts to understand either 

plant or animal lite, tor the vital processes are invariably 

ted with solutions. The ultimate unit in the 
plant i.s the cell, and the cell sap is the seat of its life; 

fresh food, too, is brought from outside always in dis- 
fbrm. In the animal, again, solutions are every - 
in evidence — to wit, the blood, the digestive fluids, 

the mine, the lymph. From the biological point of 

\iev t, the study of solutions js to be regarded si 

he utmost importance. 
One feature about solutions which is very characteristic, 

same time fairly easily detected, is the property 

liriu-ion. It must not be supposed that when we 

diss in Water and get the solution on one 

. the sugar molecules remain absolutely at rest, (hi 

the v. we have ev* ind tor believing that 

each sugar molecule, surrounded, it ma] be, bj a retinue 

onstantly moving about through the 

ml anon coming into collision with other 

molecules. We must picture a sugar solution, therefore, 

' as a SO frnafrling actixity, and the molecule 

on tin- move in every direction, limited only by the 

bom the liquid ; for they cannot ti cepi 

wh. a water-* 

In virtue of this molecular movement, it IbUowi that 

I in contact with pure 
igar in" wiD gradually distribute tl<- 

Igbout * 1 DCS of 

' ii called oontinu until 

the .! SOlul i 



FACTS ABOUT SOLUTIONS 

This may be shown by a very simple experiment, in 
which some concentrated sugar solution is put at the 
bottom of a tall glass jar, the upper part being then 
carefully filled with water. If left to themselves, the 
sugar molecules gradually penetrate the water which 
occupies the upper part of the jar, until there are as 
many of them at the top as at the bottom. This inter- 
esting phenomenon of diffusion is not peculiar to sugar 
in water ; it is characteristic of all dissolved substances. 
The rate of diffusion, however, differs markedly from one 
case to another ; for example, sodium chloride (common 
salt) diffuses three to four times as rapidly as cane sugar. 

The idea of diffusion is not new to the reader, for at an 
earlier stage we have adopted the view that the molecules 
of a gas are in constant motion, by virtue of which they 
also are ready to diffuse, to expand, and occupy fully any 
space which is put at their disposal. The magnitude of 
this diffusive and expansive force — the pressure, in other 
words — can be ascertained by interposing some surface 
in the path of the expanding gas, and thus stopping its 
further diffusion. 

Similarly, in the case of dissolved cane sugar, we may 
ascertain the magnitude of its diffusive force by inter- 
posing between the sugar solution and the water into 
which it naturally diffuses some diaphragm which shall 
allow only the water to pass, and which, like a sieve, 
shall stop the diffusion of the sugar molecules. Such 
diaphragms have been discovered, and are known as 
" semi -permeable membranes," the name having reference 
to the fact that the membrane is permeable for water, 
but not for the dissolved substance. The interposition 
of such a diaphragm between a strong sugar solution and 
water prevents the sugar molecules doing what they would 

304 



FACTS ABOUT SOLUTIONS 

naturally do — that is, fliflmfog into the water. As the 
water and the sugar solution are hound to oome into equili- 
brium somehow or other, and as the usual way of reaching 
equilibrium is barred, the principle o\' Mahomet and the 
mountain comes into play. Instead of the sugar molecules 
diffusing into the water, the latter percolates through 
the membrane into the sugar solution, and the membrane, 
if unsupported, would -turn be ruptured. The diffusive 
f the sugar thus assumes the guise of a water- 
tracting fori 

This force is known as the "osmotic p res sure " ^\' the 

up solution, and although it is rather a difficult 

quantity to measure, several successful attempts have 

ntlv been made in this direction. Hie semi-permeable 

abrane used in these interesting experiments oonaigted 

mide, deposited on and supported by 

walls of a porous pol or tube. He necessity of 

giving the membrane some such support will be obvious 

when it is stated thai the osmotic pressure of s IS per 

cent, sugar solution is 148 pound- per square inch. A 

ition has a smaller osmotic pressure; and, in 

. it baa been found that this quantity i^ proportii 

to the lution. 

Semi-permeable membranes arc not only produced bj 

chemist in 1 1 i — laboratory; ti ir frequently in 

the plan inimal worlds. A red blood corpuscle, for 

•ance, con-i delicate, flexible, semi-permeable 

skin, inside which i- a solution of the colon: .fh-r 

the blood, the ha 'in. While t In- latter i 

to pa.vs out through the en memb 

l>as» in and nut freely. The oorpi 

tin-: with :i drop <»t 

solution so] hi. mem 



: 



FACTS ABOUT SOLUTIONS 

Suppose, now, we put some blood corpuscles in pure 
water ; what result may be expected ? Obviously, if 
the contents of the corpuscle were able to penetrate their 
skin, they would diffuse out into the surrounding water. 
Owing, however, to the semi -permeable nature of the 
enclosing membrane, this is impossible. What really 
happens is that the water passes in through the skin, 
which accordingly expands as the contents increase in 
bulk. The membrane enclosing a blood corpuscle is, 
however, very delicate ; a slight increase in the volume 
of the contents is sufficient to burst it, so that the 
haemoglobin escapes and imparts its colour to the water ; 
the corpuscles are said to be "laked." 

If, now, instead of using pure water we put blooi 
corpuscles in each of several solutions of common salt 
of gradually increasing strength, we should obtain a very 
interesting result. In all solutions of less than 0*5 per 
cent, strength the corpuscles behave as in pure water, 
bursting and colouring the liquid. In all solutions con- 
taining more than 0*5 per cent, of salt, the corpuscles 
sink to the bottom, and leave a colourless liquid above. 

The explanation of this latter behaviour will be readily 
understood if we consider what would be the result of 
putting a drop of sugar solution, surrounded by a semi- 
permeable membrane, in a still stronger solution. There 
is a natural tendency, constantly at work, to equalise 
the osmotic pressures on the two sides of such a mem- 
brane, so that water will always pass from the solution 
with the smaller osmotic pressure (that is, from the weaker 
solution) to the one with the greater osmotic pressure 
(that is, the stronger solution). In the case suggested, 
therefore, water will pass from the inside of the drop to 
the outside, so that the sugar solution within becomes 

306 



FACTS ABOUT SOLUTIONS 

stroi \ blood corpuscle is affected in exactly the 

smic way when it is put in a strong solution o\' sail ; 
ctually passes out through the skin, the corpuscle 
shrink^ in giie, becomes more dense, and sinks to the 
bottom of the sail solution. 

If we were to test a number of sugar solutions of 

lually increasing strength in the same way as has 

suggested far salt, we should find that the blood 

isclefl were burst in all sugar solutions up to 5 per 

rength, but ^ank to the bottom in solutions of 

greater concentration. Par both sugar and salt, there- 
can, with the help of the corpuscles as indicators, 
piek out solutions which have the same osmotic effect 

i this point of view, a 5 per eent. solution of eane 

sugar must be regarded a- equivalent to a 0*5 per eent. 

tion of common -alt, even although the amount- of 

! matter arc so difierenl in the two cases. This 

seem rather strange, but investigations which we 

ider here have shown that the magnitude of 

the osmotic pressure fa determined, not by the weight 

of a substance which is dissolved in a given volume of 

solution, but by the number of moLiuLs present in that 

volume. Now the sugar molecule fa a rery heavy one 

so that proportionately more of this substance must be 

taken in order b definite number of molten: 

There are other interesting properties of solutio 
which are in reality closely connected with osmotic pi 

i , for instance, the (act, perhaps alreadj 

kno that a solution freezes at a lo 

temperature than wa) I s higher temperature. 

Ifoie t:. Ctenl tO which tic \\i point 

solution fa belo* - l ihrenheit, and it- boilii 

I abo\c ^l 8 . tional to the me 

1/ 



FACTS ABOUT SOLUTIONS 

molecules of the dissolved substance in a given volume. 
So that the chemist can compare the number of molecules 
present in solutions of salt and sugar by finding out the 
temperatures at which these solutions freeze or boil. 
Working on the same principle, one could get a very fair 
idea of the amount of solid dissolved in sea water by 
comparing its freezing-point with those of a number of 
common salt solutions of known strengths. The sea 
water must contain about as much dissolved solid as that 
particular salt solution which has the same freezing- 
point. 

The topic of the freezing and boiling of solutions is in 
reality closely related to the interesting question how the 
water can be separated from the dissolved substance — how, 
for example, pure fresh water can be obtained from sea 
water. The problem is not quite so simple as was 
thought by the examination candidate who suggested 
that in order to procure fresh from salt water it was 
only necessary to set aside and skim off the salt after 
standing. This method certainly works in the case of 
milk, but then milk is not simply a solution ; the particles 
of fat which separate from milk on standing are not dis- 
solved — they are only suspended, and gradually come to 
the top because they are lighter than water. 

One way, however, of getting pure water from a 
solution of salt is to freeze it ; when that takes place 
the solution does not freeze as a whole ; the solid crystals 
which separate consist of ice alone — that is, they are pure 
water. In virtue of this fact, an iceberg formed in sea 
water would, if melted, be found to yield approximately 
fresh water. Any salt which it still contained must 
have been merely imprisoned or entangled among the 
freezing particles of water. 

308 



FACTS ABOUT SOLUTIONS 

The separation of purr water from a Ball iokrtion, 

however, can be carried out not only by (reeling, hut 
by boiling. Hie latter process, indeed, is more easily 
effected, and gives a more perfect reparation; i! IS, 

therefore, used on a large scale tor the production of 

h water from sea water. Hie whole operation of 

heating the sea water and condensing the steam which 
coiner off is known as distillation, and the plant necessary 
for carrying this out is part of the regular equipment 
of an ocean liner. 

It will be obvious to the reader that one result of 
boiling a solution, and thus getting rid of some of the 
water, will be to increase the strength of the solution, 

turse, that the dissolved substance itself 

has no tendency to volatilise. Now, as already stated, 
the greater the concentration, the higher is the boiling- 
point. If, therefore, a thermometer is put in a solution, 
gar, which is boiling in an open rcoscl, the 
readings of the thermometer will get higher and higher, 
one who has made fondant for Con fe ct i onery pur- 
poses will have observed this, in this operation sugar 
and water are mixed in certain proportions in a pan 
and heated ; the temperature risei rapidly to the point 

at which the mixture begins to boil, and then slowly 
thereafter as the water is boiled off and the sugar solution 

concentrates. The subsequent behaviour of the m{ 

solution when cold varies with the extent to which this 
ration has been allowed to proa ed ; it depends on 

it which the lx)iling has l>een ^topped 
In th » bring home to the reader the 

curi' l by solutions, the p ritw has 

-I sugar or salt m the dissolved substance. These 

conn ■.• advai ly well 



FACTS ABOUT SOLUTIONS 

known to every one, but at the same time they represent 
two quite distinct classes. So far, no reference has been 
made to this distinction between sugar and salt, but it 
is one which has led to much controversy and practical 
work on the part of modern chemists, and as such deserves 
our attention. 

There are various good grounds for believing that 
the molecule of cane sugar is nearly six times as heavy 
as the molecule of sodium chloride (common salt). If, 
then, we took equal weights of the two substances, we 
should have six times as many molecules of salt as of 
sugar. Since, as already stated, the extent to which 
the freezing-point is lowered — the " depression," as we 
may call it — is proportional to the number of molecules 
or dissolved units, it follows that salt ought to produce 
a depression six times as great as that caused by an 
equal weight of sugar, provided that each is dissolved 
in the same quantity of water. Expectations, however, 
are not realised in this case, and the salt gives a depres- 
sion about eleven times as great as that due to the sugar. 
The salt, in the process of solution, seems to have yielded 
nearly twice as many dissolved units as we should expect. 
What interpretation can be given of this extraordinary 
behaviour ? 

Before any explanation is attempted, attention must 
be directed to another point of distinction between salt 
and sugar. If two wires connected with an electric 
battery were immersed in pure water, only an infinitesi- 
mally small current would pass ; the water offers an 
enormous resistance to the passage of the current, and 
may be described as practically a non-conductor. The 
moment, however, a pinch of salt is dissolved in the 
water, all this is changed, and the current experiences 

310 



FACTS ABOUT SOLUTIONS 

a comparatively small resistance. The addition of salt 
conter> on water the power to conduct the electric current, 

and the sail solution may be electrolysed as de scrib e d 

in the previous chapter. 

The ca>e of sugar is quite different. The resistance 
offered by water to the passage of a current is not 

diminished by the addition of sugar, nor can a solution 

of sugar be electrolysed. Such differences in behaviour 
as those exhibited by sail and sugar are shown by hosts 

of other substances. Of the chemical compounds which 

be dissolved in water, many, comprising acids, bases, 

and salts, behave like Bodium chloride, and are accordingly 

called "electrolytes"; the others, which, like sugar, do 
not increase the conducting power of water, are known 
i M non-electrolytes. * 

Now the curious thing is that if is just those substances 
which make water a conductor — thai is, the electrolyte 

which have an unexpectedly big effect on the free/in <;- 

point of water. This coincidence was emphasised some 

aty-five yean ago by the well-known Swedish chemist 

Arrhenius, who also suggested ao ingenious explanation. 

According to this, the molecule of an electrolyte, when 

• d in water, is liable to M dissociate, * or split up 

into two parts or "ions," one of which carries s positive 

electric- charge and the other a negative charge When, 

for insi dium chloride is added to water, the atom 

nn and the atom of chlorine which have Combined 

to form the molecule of thai substance, are instantly 
with a desire for divorce, and they separafa 

the most of the molecules ocerned, 

p;i\ ; positively charged -odium ion and r 

negatively charged chlorine ion. 

.\* finl this theory seems rather hi 

81 1 



FACTS ABOUT SOLUTIONS 

appears to be no sufficient reason why mere contact 
with water should induce sodium chloride and other 
electrolytes to commit " molecular suicide," as one critic 
has put it. The question of a motive for this " suicide " 
has been a difficulty, but recent work indicates that 
the ions have a greater affection for water than they 
have for each other, and hence arises their apparent 
readiness to part company. Whether this be the correct 
explanation or not, it is certain that the Arrhenius 
hypothesis of ionic dissociation gives an excellent in- 
terpretation of many properties of solutions, and has 
provided a basis for much valuable work. 

How, then, does it explain the fact that salt has an 
abnormally big influence on the freezing-point of water ? 
Simply in this way, that such a dissociation of sodium 
chloride as has been suggested would mean an excep- 
tionally large number of dissolved units, and since the 
depression of the freezing-point is proportional to the 
number of dissolved units, the effect of the salt on 
the freezing-point is unexpectedly great. 

Then, again, the fact that sodium chloride makes 
water a conductor of the electric current becomes in- 
telligible on the basis of Arrhenius' hypothesis. For if 
the salt solution contains a large number of positively 
and negatively charged particles, the mere immersion of 
two battery wires will cause a streaming of the +ions 
to the negative wire, and of the —ions in the opposite 
direction. Such a procession of ions carrying electric 
charges is nothing else than a transport of electricity, 
and is therefore equivalent to the passage of a current 
through the solution. The presence of the salt, that 
is, has changed the water from a non-conductor to a 
conductor. 

312 



FACTS ABOUT SOLUTIONS 

It may sound rather fanciful to talk of I pro< 

sion of ions, but ocular demonstration can be given 

of the fact that during electrolysis the positive or 

metallic part of a sail actually moves towards one elect- 
rode, while the negative or acidic part is at the siiiir 
time travelling towards the other. Pof SUcfa a de- 

monstration some coloured salt — permanganate of potash, 
for instance — must be employed. Sometime, perhaps, the 
ler may have the opportunity of seeing this very 
interesting experiment. 






CHAPTER XXVIII 

FROM SOLUTIONS TO CRYSTALS 



he 
jet 



IN the foregoing chapter reference was made to the 
curious ways in which common substances affect 
the properties of water, and to the methods of 
getting pure water from a solution. It was there sug- 
gested that by cooling a salt solution until it began 
to freeze a separation of water from the dissolved sub- 
stance could be affected, since it is pure ice which 
crystallises first. Strictly speaking, this method would 
not work with a strong solution, for cooling in this 
case might result in the separation of the salt itself 
in the crystalline form before the freezing-point was 
reached. 

This phenomenon of salt crystallisation depends on 
the fact that substances as a rule are more soluble 
in hot than in cold water. Thus, for example, a satu- 
rated solution of saltpetre (potassium nitrate) — that is, 
a solution which cannot dissolve any more nitrate — 
contains 24 per cent, of the salt at 68° Fahrenheit, 
48 per cent, at 130°, and 71 per cent, at 212°. Hence 
if a saturated solution of saltpetre were prepared at 
130° Fahrenheit, and was then cooled down, ultimately 
to 68°, it would give up as crystals all the salt which 
it contained over and above 24 per cent. In such a 
case the saltpetre is said to have "crystallised out" 
from the solution. 

314 



FROM SOLUTIONS TO CRYSTALS 

stallisation is a common laboratory operation, and 

is an efficient means of purifying salts and other sub- 

stances. This depends on the tact thai when an impure 
material is dissolved in water and crystallisation is 

allowed to take place, the separated crystals are com- 
paratively tree from impurities. These are found to 
have accumulated in the liquid which is alongside the 
crystals — the "mother liquor," as it is called, if the 
crystals are redissolved, and the process (^' crystallisa- 
tion i still purer product is obtained Some- 
times it is necessary to cany out a recrystallisatioo 
repeatedly in order to gel absolutely pure material) 

and cases are on record in which the operation has 

been performed twenty to thirty times. The reader will 
perceive, th that patience is an e ssent ial pari of the 

cbf mist's equipment. 

If a strong salt solution always behaved as it ought, 
and as we might reasonably expect it to behave, then 
when cooled to the temperature at which it ii 

it would lx'gin to deposit crystals. Hut just a- tl 

are not a lew individuals who hi peat reluctance 

to get out of bed when they OUght to he up, 10 fl- 
are so m- which exhibit a curious hesitancy bo ie 
the dissolved condition ; their solutions deposit no i 

when cooled far below- th< int. In 

these circumsta: have what is know 

saturated ** solution. 

\\Y do not require to go ■ field to find 

salt which exhibits this curious inertia. Sodium tl 

• haps, as the * k bj | the 

ographer, is a very good ca^e in point. \ 

• .11 Iv III 

a fla>k with the crystals of the -alt. adding a Little 



FROM SOLUTIONS TO CRYSTALS 

water, and then immersing the flask in hot water. This 
treatment renders the contents of the flask fluid, and 
they remain in this condition even when cooled to the 
ordinary temperature. The solution is then supersatu- 
rated, and will deposit crystals only when it is irritated 
in some manner. This may be done by vigorous shaking 
or stirring, but most certainly by dropping in a crystal 
of sodium thiosulphate itself. This operation is described 
as " inoculation v or " sowing," and it is certainly a 
sowing which produces an immediate harvest. 

The presence of an already formed crystal acts as a 
stimulus to the molecules which have sluggishly lingered 
in the dissolved condition, and they hasten to arrange 
themselves in the regular manner which is characteristic 
of the crystalline state. One result of this is that the 
contents of the flask, formerly fluid, appear to have 
become nearly solid, and another obvious fact is a con- 
siderable rise in temperature. 

This evolution of heat which accompanies the crystal- 
lisation of a supersaturated solution is not to be wondered 
at ; it is simply the repayment of a loan. For most 
salts absorb heat when they pass from the solid 
to the dissolved condition — a fact which any one can 
realise by putting a quantity of saltpetre in water and 
observing that the vessel containing the water becomes 
sensibly colder. This heat which the salt abstracts 
from the water and the containing vessel when it passes 
into solution, is duly returned by it when it comes 
out of solution ; hence the remarkable evolution of heat 
when a supersaturated solution is suddenly stimulated 
into crystallisation. 

Another substance which resembles sodium thiosulphate 
in readily forming supersaturated solutions is acetate of 

316 



FROM SOLUTIONS TO CRYSTALS 

i. Indeed its behaviour in this rasped has been 

turned to practical account in railway fool -warmers. 

When these are filled with a hot, Strang solution of 
ium acetate instead of hot wafer, the store of available 
heat is about tour times as great 

Reluctance to pass into the crystallised state is exhibited 
not only by dissolved substances, but also by ipany fi 
compounds. It is possible in the latter case to cool the 
molten substance behm its freezing-point without crystal- 
lisation setting in: the substance is said i^ be "super 

led.* As with supersaturated solutions, mere oonl 
with a crystal is sufficient to induce crystallisation. 

There i^, however, a remarkable difference in the rates 

rhicfc different supercooled substances respond t«> this 

stimulus. This is very well shown by filling a lo 

tOl tube with the supercooled liquid and touching 
one end of the column with a crystal of the solid material. 

tallisation starts immediately at the point of cont 
and is propagated through the tube at a rate which U 
perfectly regular, but differ- from one case to another. 
For instance, yellow phosphorus and benaophenone (a 
ell known to the student of organic chemistry) 
can both be obtained in the supercooled condition, but 

the rates of solidification in Hanoi tubtt are \.-i\ 
different in the two . The crystallisation of the 

,rus proo t sp ed <>? 89 in 

a second ; in the case of benaopb only 

wth of an inch per second. 
Hi ; inducing crystallisation in 

olution or in - d mbl ' 

as already indicated, the addition . of the -olid. 

But supjxj- 1 

(KMtion in which a chemist freijia nt 1 \ find- bim 



FROM SOLUTIONS TO CRYSTALS 

when he is on the track of a new compound. He may 
have actually got it before him in a solution or in the 
form of an impure oil which will not crystallise. In such 
a case, seeing none of the already formed solid is available, 
the only thing to do is to try mechanical methods of 
inducing crystallisation. If the reader has ever gone into 
a research laboratory for organic chemistry, he may have 
seen some one eagerly stirring and scratching at an oily- 
looking substance on a watch-glass. This is all with the 
object of persuading the substance to crystallise, and it is 
wonderful how frequently this method is effective. 

An excellent illustration of the way in which scratching 
promotes crystallisation is furnished by the behaviour of 
potassium bitartrate. This substance is found in grape 
juice, and is more familiar, especially to housewives, under 
the name of " cream of tartar " ; it is only sparingly 
soluble in water. If a saturated solution is made at 90° 
or 100° Fahrenheit, and is then cooled, it will be super- 
saturated at the ordinary temperature. If the solution, 
as soon as it has cooled, is poured on a glass plate, 
and the plate is scratched with a glass rod in such a way 
that the latter writes invisible letters on the plate, the 
writing soon becomes visible, because specially rapid 
crystallisation is induced along the lines where the glass 
rod and plate were in contact. The letters are traced 
out by the deposited crystals. 

When a salt crystallises out from its solution in water 
it frequently happens that it carries water along with it. 
In the act of crystallisation each molecule of the salt 
hooks on to itself one or more molecules of water. This 
is not a mere mechanical adherence, for the crystals may 
be removed from the solution, and pressed between 
blotting-paper until they are absolutely dry, without 

318 



FROM SOLUTIONS TO CRYSTALS 

detaching any of these water molecules. Tin 
matter off fact, chemically combined with the Bah to form 
a composite molecule, and they will not be drawn by 
methods which suffice to dry op ordinary moisture. 
w iter which is held by ■ Bah in this way is described m 
iter of crystallisation." 
Although blotting-paper fails to effect the separatioq 
of a >alt and its watn* of crystallisation, tlu' bond <>f 
union is really not very strong and it may Ik- -aid thai 
the love between the two grows cold as the temperature 

So that by merely wanning a salt which eont 

r of crystallisation, the water is driven off as vapour, 

and finally the -alt alone — the "anhydrous" -ul t , a- it is 

called — is left 

Water molecules, h o w eve r , air not all alike in the 
icity with which they cling to the sail molecule 

in lx- detached only by the application of a higher 

temperature than i- required for other-. Of this graded 

affection blue vitriol — or copper sulphate, to give it iti 

nical name — furnishes an interesting example. The 

inary crystals of this substance are blue in colour, and 

contain 36 per cent, of their weight of watt; 

molecule of the salt carries with it five moleculei of m 

tllwition. If the crystals are reposed for boom 
to the temper a t ur e of 218 Fahrenheit, Bay in a 

steam oven, four out of the five molecules L ro of!', and the 
de blue. The la-t mofecuk i- nmiv faithful, 

a rise of te mp er a ture to WO oompeh even tin 
to t Leparture, and a white powder ii left ai the 

OUS salt. 

In cases the Is of water in a crystallised 

salt begin 

the ordinary temperature \ don this 



FROM SOLUTIONS TO CRYSTALS 

curious behaviour is available, for washing-soda, which 
normally contains ten molecules of water of crystallisation 
to each molecule of sodium carbonate, loses some of them 
on mere exposure to the air. This process is revealed to 
the observer by the fact that the crystals of washing-soda, 
originally clear and transparent, become gradually opaque, 
as if a white powder had been deposited on them. This 
is due simply to the partial removal of water from the 
surface layer of the crystals, which therefore exhibit signs 
of disintegration. 

In blue vitriol an instance has already been cited of the 
way in which the colour of a given salt varies according 
to the number of molecules of water of crystallisation 
which it contains. An even more striking example of 
this phenomenon is furnished by a substance known to 
chemists as magnesium platinocyanide. This salt can be 
obtained with seven, six, or two molecules of water, as 
well as in the anhydrous state, and these various products 
are respectively scarlet, lemon-yellow, colourless, and 
orange -yellow. 

The extraordinary influence which water thus has in 
altering the colour of a salt explains the action of the 
so-called " sympathetic " or " invisible " inks. One of 
these is a solution of cobalt chloride, a salt which 
crystallises with six molecules of water in the form of 
dark red crystals ; the anhydrous salt, on the other hand, 
is deep blue in colour. The water solution of cobalt 
chloride is merely pink, and if this is used to write on 
paper instead of ordinary ink, the impression left is so 
slight as to be scarcely noticeable, even when it has dried. 
The application of heat to the paper, however, makes the 
writing immediately visible, for the cobalt chloride is 
thereby converted into the blue anhydrous salt. Curiously 

320 



FROM SOLUTIONS TO CRYSTALS 

enough, it* left to itself, the writing fades away, for the 
blue salt gradually absorbs moisture from the air, re- 
generating the pink salt, which is almost invisible. 

On the same lines the reader will himself be able to 
explain the behaviour of certain artificial flowers which 

I to be made in Paris. Their petals are tinted 
with eobalt chloride, with the result that while the tin 
are usually of a rose colour, they turn blue in a very dry 
atmosphere. 

Nothing has as yet been said about the strikingly 
regular and beautiful forms in which dissolved substances 
crystallise out from their solutions. These must be seen 
to be appreciated Asa rule, each dissolved salt separates 
in a definite shape, peculiar to itself, and it is, in feet, 
this regularity of form which is the main distinguishing 
of the crystalline state. If the separate crystals 
large, it not only to see distinctly the various 

vhii. but also to count them, and w hen the chemM 

become familiar with the crystalline habits of a 
substance, he can afterwards identify it, even 
amongst many other-, merely by its appearance. 

The pro crystallisation consists in an ordered 

fitting and pad ether of the molecules of the solid 

:neiit is i*\ ideiit not only from 

e, well-formed crystals, but also from the 
app under the microscope of minute quantities of 

itallised solutions, If, for instance, a drop of am- 
monium chloride solution is crystallised under a microscope 

on close < lamination to h 
assun gular fern-like shap< I in. 

eader musl n<»t suppose that it h onlj 6am 
ind other similar liquids thai 
i 



FROM SOLUTIONS TO CRYSTALS 

solidify to crystalline masses, but, in addition, we must 
be prepared to think of crystallisation as having taken 
place from solvents which are solid at the ordinary 
temperature. A fused alloy, for instance, containing a 




Fig. 14. — Crystals of sal ammoniac which have separated out 
from solution in water ; as seen under the microscope. 

little of one metal dissolved in another, is quite analogous 
to a solution of a salt in water, although the alloy must 
be kept at a very much higher temperature, if it is to 
remain in the liquid condition. Now just as the salt 
crystallises out from its water solution, so the one metal 

322 



FROM SOLUTIONS TO CRYSTA1 S 

out from the fused alloy. The dif fe rence is 
that in the alloy we cannot tee the crystals which were 
fanned firsts because the alloy as ■ whole baa subsequently 
tifiedi In fact, an alloy which has crystallised and 
baa then been cooled down to the ordinary temperature 
i^ similar to what a -alt solution would become it' it were 
cooled a long way below the freezing- point of water. In 
the latter circumstances we should not he able to see the 
salt Crystals because of the masses of ice with which tin v 
surrounded 

In >pite of this difficulty, there are ways and DM 

hat sort and shape o\' crystals have primarily 
separated from an alloy. In a few eases tin- Bant) 

r\iceable, by virtue of the fact that metals 
difler in their permeability to these ray- ; some metals 
are transparent to the ray-, othf Opaque. 

9 ippose, for insts had a -mall quantity of golds 

which i^ opaque, dissolved in a large quantity of sodium, s 
metal which i- comparatively transparent to the Rfintj 

Such an alloy if fused would be comparable with a 
dilute solution of a sail in water. In this latter i 

•n is dilute, the primary crystallisation on 
ing would consist of ice; similarly, the (used alio] 
cooled, would deposit -odium. That is, the first crystals 
in the alloy would con-i-t of the metal 
h is t: lit to the Rontgen rays, while the 

spaces bet we en these crystals would ultimate!) con' 

the gold, which crv-t;tlli-» I 

the better will be the opportunity far the prim 

row large. 
It tion of ' 

top of ■ light-1 i sensttta 

and exposed to th these are able to pass 



FROM SOLUTIONS TO CRYSTALS 



through the primary sodium crystals and act on the 
plate, but are blocked to a large extent by the opaque 
gold in the spaces between the crystals. The impression, 
therefore, obtained on the plate differentiates between the 
primary crystals and the rest of the alloy. 




Fig. 15. — Crystals which have separated from a fused alloy 
of copper and tin ; as seen under the microscope. 

This extremely interesting method of studying the 
crystalline condition of alloys can obviously be employed 
only when there is a fairly well-marked difference between 
the two metals in relation to the Rontgen rays ; the 
scope of its application is therefore somewhat limited. 

324 



FROM SOLUTIONS TO CRYSTALS 

Another way of revealing the crystalline oonditioa o( 
an alloy is to cut a section, polish one of the surfaces, and 
treat it with an acid. This treatment brings out t he 
detail^ of the crystalline structure, and with the help of 
microscope and camera a photomicrograph is obtained, 
the surface of the alloy being illuminated by either oblique 
Or refle ct e d light. Ulis method is not restricted in its 

pe like the previous one, and it is largely applied at 
the present time, notably in the investigation of the 

character of iron and steel which have been exposed to 
different conditions (compare Pig. 15), 

Working on these lines, the modern chemist can do 
v marvellous things in the way of deciphering the 

of an alloy. The tale is on the inn' of it, if 

but the key to the language, and the w 
patience. As aids he requires chiefly two instruments 
which in countless directions are invaluable to the scientific 
worker. It is indeed difficult to realise ho* much poo 

would be to-day had we no mi< 
and no i 






CHAPTER XXIX 
GREAT EFFECTS FROM SMALL CAUSES 

IT is a commonplace to say that incidents or persons 
may have an influence quite out of proportion to 
their apparent value. This is what every one learns 
sooner or later, but it is worth while noting here how 
very remarkably this principle is enforced by many facts 
with which the chemist is familiar. Nature herself, in 
various striking cases, reminds us that what is apparently 
insignificant is frequently of the utmost importance. Take 
the case of carbon dioxide ; this gas is present in the 
atmosphere to the trifling extent of 3 parts in 10,000, 
and yet it is on this that the whole vegetable life of our 
globe depends. As was pointed out in a previous chapter, 
it was not until the existence and significance of this 
Txnrths of 1 per cent, of carbon dioxide were appreciated, 
that the miracle of vegetable growth could be rightly 
interpreted. 

Modern chemistry furnishes many remarkable instances 
of the way in which the history of a chemical change or 
the behaviour of a particular substance is profoundly 
modified by the presence of small quantities of foreign 
material. It is not necessary to go far afield in search of 
such cases, for water, one of the commonest chemical 
compounds, has recently been shown to have an extra- 
ordinary influence in promoting chemical action between 
other substances. 

326 



SMALL CAUSES; GREAT EFFECTS 

The reader ifi probably familiar with the experiment in 
which a lighted taper is brought to the mouth of I lodft- 

water bottle containing a mixture of hydrogen and < 

A vigorous action, marked by a Violent explosion, takes 

place between the md water i- produced Hie 

striking liberation of energy which accompani< fl the chemical 
action between hydrogen and oxygen 18 evidence of the 
- me eagerness of the two elements to "go for* I *cfa 
other. Vet, if care is taken to remove all trace* of 
moisture from the original gases, thll fast of battle has 
apparently gone. A tube containing a mixture of per- 
fectly dry hydrogen and perfec t ly drj oxygen may be 
Strongly heated without the content a explodii dly 

binding result. 
It has been put on record that in twelve >ueec>.sive 

• riments on pair- of tubes, one of each pair containing 

perfectly dried hydrogen and oxygen, the other containing 

the imperfectly dri- ill of heating tl 

to redness in a Bun-en burner was invariably the same ; 

ther in explosion in the tube containing the im 

fectly dried gasi -. but no explosion in the other. It 

i^ true that in on], ire this result the ga-es in the 

latter tube had b« \ carefully dried for ten di 

but this does not detract from the striking chai 

the experiment-. 

1 for ten days ! w tl xclnini ; M fa 

i> that doner"' Hi mu-t, oJ from Ul 

mind tl i-inp any ordinary methodi «>f drying 

u can l>< dried only by letting i f c 

in contact with BOOM material wbiA lias an b 'nd- 

ne&s 1 whiVh will readily absorb it irf 

(juiekl 

•ng ralphuri uid phosph b . 



SMALL CAUSES; GREAT EFFECTS 

In the experiments just described the condition of 
perfect dryness was attained by putting some phosphoric 
oxide in the tube along with the hydrogen and the oxygen. 
The oxide in these circumstances acts like so much bird- 
lime, and any water molecules that are flying about are 
gradually caught. In the absence of water molecules — 
the mischief-makers, we may term them, or shall we say 
match-makers ? — the hydrogen and the oxygen are quite 
callous to each other. So soon, however, as the merest 
trace of moisture is admitted into the tube, the contents 
will explode when heated. A few water molecules, in 
fact, are responsible for all the difference between peace 
and war, or between the single and wedded states — accord- 
ing to the way in which the reader prefers to picture the 
interaction of hydrogen and oxygen. 

This extraordinary influence of water on chemical change 
is so remarkable that it is worth while to refer to another 
interesting experiment that has been made. As the reader 
is aware, ammonia is a colourless alkaline gas, whereas 
hydrogen chloride is a colourless acid gas. Like alkalies 
and acids in general, these two gases interact, forming a 
salt — ammonium chloride or sal ammoniac — the character- 
istic and curious feature of the process being the production 
of this white solid substance from two colourless, invisible 
gases. It turns out now that this combination between 
ammonia and hydrogen chloride, which takes place so 
readily under ordinary circumstances, is not observed when 
the gases have first been completely freed from all stray 
water molecules. 

The ordinary incandescent mantle is an excellent example 
of the value which may attach to small quantities of foreign 
material. The mantle consists to the extent of 99 per 
cent, of thoria, which is the oxide of the metal thorium, 

328 



SMALL CAUSES; GREAT EFFECTS 

and is obtained chiefly from mona/ite Band, bund in 
Brazil and in the United Statea The remaining 1 per 

cent, of the mantle is ceria, the oxide of the rare metal 

cerium, and, in spite of its small proportion, it is on this 

admixture that the virtue of the mantle wholly depends. 

tle> composed o\' pure thoria alone would be of no use, 

hen put in a Bunsen Maine they give out only a dull 

light. On the other hand, if more than 1 pel* ceni. of 

i is added to the thoria a less brilliant effect i^ obtained ; 

it i<, in tact, possible to have too much of a good thing. 

\ only ha- this paltry 1 per cent, of ceria made the 

incandescent mantle a brilliant success; it has indirectly 

been the salvation of the pas industry. In competition 

with electricity, gas would have been badly beaten as 

a source of light had it not been for the discovery of 

the incandocent mantle. By it- agency the illuminating 

power of a cubic foot of coal gas is enormously increased. 

er interesting fact in connection with the in- 

lo so cn t mantle deserving of passing notice i- the 

Meet which the rapidly increasing use of 

thorium nitrate had on the price of that article. Early 

in 1894, an ounce of thorium nitrate sold tor 55& ; by 

Januarj L895, on account of competition and improved 

met! production, the price bad fallen to £5s., by 

Jul] to 1 ta., by November of the same year to 

I mother ni month- the pri In halved) while 

at the | time it ha- fallen to about Ls. Seldom 

any chemical product und< ocfa a rapid 

change in price. 

A interesting illustration of the extraordinary 

ience exerted by mall quantities of foreign matter 
I by Mm b< haviour of certain phospho 
substances. A: the tulphides of the a* 



SMALL CAUSES; GREAT EFFECTS 

barium, strontium, and calcium, and, as the name " phos- 
phorescent " implies, these sulphides are luminous in a 
dark room after they have been brought out of the light. 
Luminous paints or luminous compositions generally are 
dependent for their characteristic behaviour on the pre- 
sence of such a phosphorescent substance. Curiously 
enough, however, the pure materials do not appear to 
be phosphorescent ; it is only when minute traces of other 
matter are present that they are stimulated to luminous 
activity. 

Incandescent mantles and phosphorescent substances 
illustrate very well the striking modifications of properties 
which are attributable to small quantities of foreign 
material. But it is not only the properties of particular 
compounds which are affected by impurities ; as we have 
seen in the case of imperfectly dried hydrogen and 
oxygen, the speed at which a chemical change takes place 
may be remarkably modified by the presence of some 
alien substance, which keeps, so to speak, in the back- 
ground, and does not itself suffer any apparent alteration. 
Such an acceleration of chemical change by an alien 
substance is known as " catalysis," and the alien substance 
itself is spoken of as a " catalytic agent." 

Chemical changes which take place under the influence 
of a catalytic agent are not merely laboratory curiosities — 
they are of the utmost importance in the technical world. 
The most modern method of manufacturing sulphuric 
acid, for instance, depends on just such a change, and 
if the reader tries to realise the fact that about 3000 
tons of sulphuric acid are made in England every day, 
he may appreciate the bearing of catalysis on chemical 
industry. The main thing to be done in making this 
important product is to persuade sulphur dioxide — the 

330 



SMALL CAUSES; GREAT EFFECTS 

suffocating ga- which is produced when sulphur is burned 
— to combine with more oxygen. This will not occur 
spontaneously when ih are merely mixed, even at 

a high temperature. They mu-t be brought into con- 
tact with some third substance which plays the same 
part a> water does in the combination of hydrogen and 
oxygen. 

In the case oi' sulphur dioxide and oxygen the third 

party, which act- in some subtle way as mediator between 

the other two, is platinum in a finely divided condi- 

This metal has quite a reputation tor accelerating 

chemical actions in which it is not directly involved : it i< 

a sort of chemical busybody. There is a well-known 

periment which illustrates this characteristic of platinum 

clearly indeed. A roll of platinum foil i- suspended 

in the flame of a Bunsen burner until it is red hot ; the 

is then turned off, and immediately turned on again, 

but not lighted. The observer sees that the foil, which 

ool down whenever the gas was turned off, 
begins to glow afresh, although there is no visible flame ; 

main- in this condition SO long as the mixture of 
air and gas from the burner is allowed to How over it. 
What ha- happened i- that the platinum induces the 
slow combustion of the gas, and it is the heat given 
out in this process which keep- the metal visibly hot. 

platinum it-elf i- not affected, -<> that we have here 

DOeUent example of catalytic action. 
A -imilar part i- played by the finely divided platinum 
in the modern method of making sulphuric acid — the 

•■>-. a- it is appropriately called. I Y 
the | of the Catalj f : DH- 

pcratiire of about 500 Fahrenheit, sulphur dioxide and 
readily unit mn another compound named 



SMALL CAUSES; GREAT EFFECTS 

sulphur trioxide, which need only be dissolved in water 
to produce sulphuric acid. 

This sounds all very simple, and, in fact, this way of 
making sulphuric acid was discovered long ago. It 
could not, however, be employed on the manufacturing 
scale, as the platinum turned out to be very sensitive 
to impurities in the sulphur dioxide, and gradually be- 
came ineffective. Ways and means, however, have now 
been discovered for thoroughly removing the impurities 
and keeping the platinum in good condition, so that 
what for long was merely a laboratory experiment has 
now become the basis of a very important manufacturing 
operation. The " contact " process is rapidly coming 
to the front, and bids fair to oust the old and cumbrous 
method of manufacture, the prominent feature of which 
is the use of huge leaden chambers. 

In recent years platinum has been prepared in another 
condition in which it exhibits remarkable catalytic act- 
ivity, namely in solution in water. It may seem to the 
reader rather absurd to speak of dissolving a metal in 
water, as if it were so much sugar or salt, but it is indeed 
a fact that, by the help of the electric current, platinum 
has been got into water in such a state that it closely 
resembles a dissolved substance. If two pieces of stout 
platinum wire are immersed in water so that their points 
are very close together, and an electric discharge is passed 
across the intervening space, the water gradually assumes 
a deep brown colour, and is found then to contain platinum 
in solution. At least it seems to be in solution, for the 
liquid may be filtered through a piece of blotting-paper 
without leaving any particles behind, and it may be 
kept for a long time without depositing any sediment. 
On grounds, however, into which we cannot go here, the 

332 



SMALL CAUSES; GREAT EFFECTS 

ifl adopted that this platinum solution is ivalb a 
suspension of exceedingly minute particles, s ( > tinv thai 
thi v can find their way through the pores of filtering- 

paper. 

However that may be, there is no doubt that platinum 
in t In— condition is intensely active from tin- catalytic 
point of view, as shown, for instance, 1>\ its effect in 
tting the equilibrium of hydrogen peroxide Hiii 
is a substance which, in water solution, is applied a 
bleaching agent for hair, ivory, and old pictures, Chemi- 
cally, it is a very interesting substance, being closely 

related to water; it» molecule-, in fact, 18 a molecule 
of water, to which an extra atom of oxygen ha- been 
tacked on. The attachment, however, is not very secure, 

ami tin- result is that hydrogen peroxide U readily de- 
composed into water and oxygen. This chemical action, 
• imposition, is accelerated in quite a remarkable 

aer by the addition of a little platinum solution 
In hydrogen peroxide. Thus it' we were to take 

dilute hydrogen peroxide and add to it so much platinum 
solution that a pint of the mixture contained li of 

an ounce of platinum, the decomposition of the hydro 

Mild lie complete in about two hours; if no 

i platinum solution were added the hydrogen peroxide 

Id lose practically none of its OXygeU in that lime. 

Perhaps a still more convincing proof of the catalytic 
pow. -lis platinum solution is obtained by 

! it iii a flask with a mixture of hydrogen sad 

In ordinary circumstances the-r twu 

itrongly heated before they will combine 

platinum solution they unite nt Hk 
lowly but steadily and with 



SMALL CAUSES; GREAT EFFECTS 

extraordinary thing is that a minute quantity of platinum 
is able to bring about the combination of very large 
quantities of hydrogen and oxygen. One experiment has 
been recorded in which, under the influence of the 
TeircTuth of an ounce of platinum, over two gallons of 
a mixture of hydrogen and oxygen disappeared in seven- 
teen days. And the platinum was as active at the 
end of this period as at the beginning ! 

There are numerous catalytic agents in addition to 
those which are used in the laboratory or the factory. 
Our bodies are the scene of many chemical changes which 
are promoted and accelerated by the influence of certain 
agents called enzymes, the exact nature of which is not 
yet know T n. These substances play an important part 
as catalytic agents, notably in the processes of digestion, 
but an excursion into this interesting field would take 
us too far. Perhaps enough has been said to convince 
the reader that in chemistry, at least, much that is 
apparently insignificant is of the greatest value and 
importance. 






334 



CHAPTER XXX 

HOW TRIFLING OBSERVATIONS LEAD TO 
GREAT DISCOVERIES 

TEDS scientist who is advancing into the unknown 
ts out with the object of searching foi 
tnething which hi> theories lead him to believe 

be found in the unexplored region just ahead It 
frequently happens, however, thai a- lit- iteadilj plod 
forward he discovers something bv the way which u 
much greater importance than the ultimate I of hi 
search. The story of the ways in which some nidi un- 
expected discoveries have been made is interesting, if not 
romantic, and the rehearsal of one or two M these will 
show the reader 1h>w much depends sometimes on s casual 
occurrence, and on the observer^ readiness to note v . 
happen> and to take advantage of it. 

1 . the important element which 
farms one-fifth by volume of the air, wai made in a 
casual sort of fashion about 140 i tV . 
we are told, wai vety proud of s burns 

had come into his pOOBCSSIOnj and was going round 
laboratory one day concentrating thr Km'fl rays with tin 
lens, and focussing them on all sort- of -ul>stances. 

Og the material- which he thus happened to 
to the heat of the eoiuvnl 

urv, which. do* kno Ij plit up 



GREAT DISCOVERIES 

by heating into its constituent elements, mercury and 
oxygen. 

Priestley observed that a gas was given off from the 
mercury oxide, and when he had collected some of the 
gas he was able to show that a candle burned in it with 
a remarkably vigorous flame. To Priestley this was some- 
thing quite new and fascinating ; as he says himself, 
" This surprised me more than I can well express ; I was 
utterly at a loss how to account for it." Further experi- 
ments showed him that the gas " possessed all the pro- 
perties of common air, only in much greater perfection.' 11 
He had, in fact, discovered oxygen, and all as the result 
of curiosity about the powers of his newly acquired 
lens. He was, it is true, on the look-out for new 
gases at that time, but, after all, the concentration of 
the sun's rays by a lens is a most unusual way of 
producing heat, and would not naturally be chosen for 
that purpose. 

If, however, the investigator's mind is occupied with 
a definite subject, it is wonderful how the most trifling 
occurrences are seen by him to have a bearing on the 
problem and are made to contribute to its solution. So 
it was with Priestley, and so it has been in many other 
cases which might be quoted. 

One of those which has been put on record occurred 
in connection with the discovery of blasting gelatine by 
Nobel. As has been stated in a previous chapter, the 
dangerously explosive substance nitro-glycerine cannot by 
itself be safely handled and transported. The difficulty 
may be got over by soaking up the liquid nitro-glycerine 
into Meselguhr, and so converting it into the product 
known as dynamite. It was obvious to Nobel that this 
operation involved a reduction of the explosive force of 

336 



GREAT DISCOVERIES 

nitro-glycerine. for the absorbent Jciesdgtshr is a neutral, 
harmless, non-explosive material So. although it ran 
up as much as three times its quantity trf nitro- 
glycerine, the explosive power of the latter is lowered 
one-fourth. Nobel was therefore anxious to find as 
a substitute for kieselguhr some substance which would 
convert nitro-glycerine into a form suitable tor Baft 
handling and transport, and which at the same time, 
being itself explosive, would not diminish the effectiveness 
of the nitro-glycerine. 

The discovery of a material with the desired pro p e rt i es 
came quite by accident. Nobel cut hi- finger one day 
in the laboratory, and procured some collodion to paint 
the cut and SO form an artificial protective -kin. 
I lodion, it should be stated, i- a solution of a sub- 
stance resembling gun-cotton in a mixture of alcohol and 
ether; as these two liquids are very volatile, a film of 
dion exposed to the air soon dries up and forms 
a skin. 

After Nobel had used a little of the collodion to paint 

the wound, it occurred to him to pour what was lefl 

into a vessel containing nitro-glycerine lie did tin'-, and 

rved that the collodion mixed with the nitro-glycerine 

formed a jell-dike ma—. Thi> little observation 

to -how him the way in which the problem 

of t; dguhr by a more active SUb- 

oould be solved Experiments were carried nut 

. and these led to the manufacture of the 

I explosive know gelatine, which is a mixture 

of nitro-glycerine and one pari of soluble 

ton. Pure blasting gelatine is so violent in it 

■ it cannot be on d exo pi for th 

of the 



GREAT DISCOVERIES 

St. Gotthard tunnel. For ordinary practical purposes, 
however, the explosive power of blasting gelatine is 
modified by introducing a certain amount of non-explosive 
absorbent material. 

Some discoveries have actually been made through an 
accident happening to the apparatus with which experi- 
ments were being carried out. This was the case with 
one important series of investigations into the behaviour 
of gases ; and the famous chemist Graham has explained 
what it was that led him to make his wonderful experi- 
ments on gaseous diffusion. It appears that an earlier 
worker, Dobereiner, had occasion to prepare large quan- 
tities of hydrogen, and one day accidentally used as gas- 
holder a glass jar which had a tiny crack in it. 

Now it is a well-known fact that if an undamaged 
glass jar or tumbler containing hydrogen or air is in- 
verted in a dish of water, so that the level of the water 
outside and inside the jar or tumbler is the same, then 
no appreciable change will take place in the position of 
the water-level, even after a considerable time. But 
Dobereiner, to his great surprise, found that with his 
cracked jar inverted in water and containing hydrogen, 
the water gradually rose inside, If inches in 12 hours, 
2f inches in 24 hours. 

It was left to Graham to give the correct interpreta- 
tion of this very striking observation. He showed that 
hydrogen, as the lightest known gas, can get through 
minute apertures more rapidly than any other gas, so 
that what occurred in Dobereiner's cracked glass jar was 
an escape of hydrogen from the inside to the outside, 
accompanied by a slower entrance of air through the 
crack. As the hydrogen escaped more rapidly than the 
air got in, the pressure of the gas inside the jar was 

338 



GREAT DISCOVERIES 

lowered and the level of the water rose. Thus it was 
that the use of a cracked vessel instead of a sound one 
led on to Graham's famous investigations on the diffusion 
of gases. 

A more recent and equally striking instance of a 

breakage leading directly to a valuable d i scovery has beet) 
recorded in connection with the manufacture of artificial 
indigo — a manufacture which, as we have alreadv Been, 
famishes a conspicuous ease of the chemist's sucoeesfb] 
attempt to build up natural products, and to compete 
with Nature herself 

One of the most important steps in the manufacturing 
process is the production of phthalic acid from naphtha- 
— the chief raw material of synthetic indigo. This 
change can be effected by the action of hot sulphuric 
I upon naphthalene, but only slowly. In the course, 
however, of experiments carried out with the object of 
improving the method of converting naphthalene into 
phthalic acid, the bulb of a thermometer WBM accident- 
ally broken, and the mercury ran out into the heated 
mixture. It was at once noticed that in presence of 
mercurv the conversion of naphthalene into phthalic 
acid was much accelerated, and this chance observation 
at once to the desired improvement of the pfOO 

•of mercury at this stage of indigo manufacture 
is now an established c u sto m . 

The reader must, of cour-e, remember that without 
[Uate knowl irt of the inve-tigator and 

without keenne— of observation these chance occuiiv! 

been of no account. The ven 

supposing lie 1. msry equipment) must all 

be on the look-out for wh 

always eager to see NatUM in unfamiliar gaib. 



GREAT DISCOVERIES 

The difficulty is that people sometimes make a valuable 
observation without attaching importance to it. It may 
be difficult to bring their new discovery into harmony 
with what they already know, and so they come to the 
conclusion that their observation must have been wrong, 
and that their senses must have deceived them ; or else, 
by some forced explanation, they seek to fit the newly 
observed facts into some of the mental pigeon-holes 
which are already available. When such difficulties crop 
up, the remedy is to have recourse to fresh observation 
and to collect more facts. 

In this connection there is an interesting story of 
Liebig, whose fame as a chemist rests on many other 
things than extract of meat. On one occasion he pre- 
pared a liquid which in many of its properties resembled 
chloride of iodine, although in other respects quite 
different. He was struck by the differences, but, without 
making any further experiments, devised an explanation 
which satisfied him at the time. He was at least 
sufficiently satisfied to label the bottle of liquid " chloride 
of iodine. " The reader can imagine Liebig's disappoint- 
ment and chagrin a few months later when he heard of 
the discovery by a Frenchman of the new element 
" bromine," and realised that it was this element which 
he had had before his eyes all the time and had labelled 
"chloride of iodine.''' Liebig tells the story himself, 
and quotes it as showing the result of adopting explana- 
tions not founded on experiment. 

As an example of the persistent and successful follow- 
ing up of puzzling observations by further experiments, 
nothing better can be quoted than the work which led 
to the discovery that there was in atmospheric air a 
gas, the presence of which had not previously been 

340 



GREAT DISCOVERIES 

suspected. That argon, as thi^ gas la now called) 
should have so Long remained undiscovered, is due to 
the fact thai it is extremely similar to nitrogen ; i\ 
therefore, difficult to find any way of distinguishing 
and separating the two gases when they are mi 
ther, as in ordinary air, \ a matter of tact, argon 
tther heavier, bulk for hulk, than nitrogen, and it 
was thi^ slight difference which Lord Rayleigh observed 

and followed Up. 

Suppose the reader tries to realise ho* very anal] 

the difference in weight actually o b s er ved The 

globe which Lord Rayleigh used in weighing 

tilled, firstly, with nitrogen — "atmospheric" nitrogen — 

I from air by removal of oxygen, moisture, and 

boo dioxi Uy, with nitrogen prepared Brora 

various chemical compounds. Although these two samples 

Id naturally I to exhibit the same behavio 

the atmospheric " nitrogen filling the 

in heavier than the weight 
grains) of the " chemical 11 nitrogen filling the same 

globe. Tlii- i- obviously quite a -mall ditl and 

probably many in\ on would have attributed the 

disa to some error in their experiments, and 

thought no more about it. Not so Lord Rayleigh; 
after showing that numerous possible sources <-i error 
[eluded, he led, in I Hon with Pko- 

fesso l; ing and examining tip 

which i- respu ht <»t' 

pheiic "" nitrogen a- compared with "chemical" nitro| 
I rom all this tin- reader will see what a high value 

close and tru-twortl, vatlOO SVeO of 

tritl ttlS ami CO 

U very well, but what is primarily essential 



GREAT DISCOVERIES 

for the true investigator is the learning and observing 
attitude towards Nature. Any one, indeed, who cultivates 
the habit of careful and patient observation rediscovers 
many things for himself, and may hope to add his 
contribution to the romance of science. 









842 



I N D E \ 



191 

Alcohol. 

Alizaric, ! 

Alkal 

Alkalis, 88 

Alkal 

AUotropic fore 

Alio; 

Alun 

Ammonia, 90, 186, 186 

Ammonia from coal. 1 1 5 

Ammonium >ulph.v J81 

Amorphous substance*. 

Analysis. _ 

Antipyrine, 288 

Archimedes, LSI, J 

Ifl exploration. 1 9 I 
Argon, 341 

■ . 
Arsenic m beer 
Artificial camphor. 1 

diamonds, 54 

dyes, 1 

ivory, I 



Atom- 

Aurora ItaifUlil. II 4 

B 

Baku. 

Barium ox: V I 5 

■ 

Beet sugar. 

Benz. 187 

Black 

Black 

Bleaci 

i 

Boiling-point of solutions, 

308 
Bone 
Boric I 

170 
'U0 
Bunsen and Kirchhoff. 1 

n burner, 1 1 1 
Burning glMt, 1 1 1 



Calcium Oftl 

| 









INDEX 



Candles, 45, 107, 244, 245, 

246 
Cane sugar, 228, 229, 230 
Carbamide, 250, 251,253 • 
Carbides, 137, 200 
Carbohydrates, 227 
Carbolic acid, 284 
Carbon, 53, 114 
Carbonates, 86, 94 
Carbon dioxide, 43, 108, 116, 185, 

217, 270, 271,326 
Carbonic acid snow, 185 
Carbon monoxide, 45, 152 
Cast-iron, 63 
Catalysis, 125, 330, 331 
Celluloid, 235, 236, 256 
Cellulose, 132, 235 
Ceria, 329 

Charcoal, 53, 57, 171, 230 
Cheese, 228 

Chemistry and electricity, 290 
Chili saltpetre, 202, 224, 249 
Chocolate, 265 
Coal, 131 

Coal gas, 145, 148 
Coalite, 150 
Coal tar, 283, 289 
Coal Tar Jubilee, 287 
Coins, 75 
Coke, 147, 149 
Combustion, 107, 115 
Combustion, spontaneous, 127 
Commercial chemistry, 249 
Compounds and mixtures, 33, 

77 
Contact process, 331, 332 
Copper, 71, 299 
Cream of tartar, 318 
Creosote oil, 283 
Crookes, Sir William, 202 
Crystalline substances, 53 
Crystallisation, 314, 315 
Crystallisation in metals, 322, 

323 



D 

Daniell cell, 292 

Davy, Sir Humphry, 163, 297 

Dead Sea, 101 

Destructive distillation, 142 

Detonator, 175 

Dewar, Sir James, 187, 190 

Dextrin, 234 

Diamond, 53, 54 

Diffusion, 303, 304, 338 

Discovery of argon, 341 
,, ,, bromine, 340 

,, ,, caesium, 213 

,, ,, helium, 213 

,, ,, mauve, 285 

,, „ oxygen, 336 

,, ,, rubidium, 213 

Dissociation, 194 

Distillation, 101, 194 

Distillation of coal tar, 284 

Dobereiner, 125, 338 

Draught, 109 

Drying gases, 327 

Drying oils, 240, 241 

Dynamite, 178 

E 

Edible fats, 239, 240 

Egg substitutes, 267, 268 

Electricity and chemistry, 290 

Electricity v. gas, 283, 329 

Electric furnace, 197 

lamps, 69, 70, 71 

Electrolysis, 297, 298, 299 

Electrolytes, 311 

Electro-plating, 74 

Elements, 30 

Elements in meteorites, 205 

Elements in the sun, 212 

Emery, 257 

Endothermic processes, 168 
I Energy in coal, 152 
I Engraving on metals, 82 

344 



INDEX 



Bpsom salts, 1<>.> 

Exc* -•■>. 1 • ^ 

F 

Kara 

Firc-alain:*. 76 

I 

• 

I 

DM caps, 1 
and steel 
Food preserva 
Foo* 

Fntnkl.ti.], 1 - 

Freezing of rac 

F reeling point* of alloys, 78 

Freezing- point of solution- 

m 



Olhani'cH iron. 7.;. 117 

Gaaes ar 47 

Gas 

Graham. 
Ora| 






ciu! I . ;.. L76 

Gunj •• 171 

H 

5 i 

818 

1! 

gen pero 

I 

1 8 1 

oga, 104 

K 

•!., |] \ 

L 

I 

i 

■ 



INDEX 



Liquid air, 186, 188, 190 
,, helium, 191 
,, hydrogen, 186, 190 

Liquids and gases, 47 

Lubricating oils, 242, 243 

Luminosity of flame, 158 

M 

Madder root, 253, 254 

Magnesium, 114 

Manures, 223, 224, 225 

Margarine, 239, 264, 265 

Marsh gas, 132 

Matches, 121 

Mauve, 285 

Mercury, 22 

Mercury fulminate, 167 

Metals distilled, 194 

Meteorites, 205 

Methylated spirit, 144 

Mice in poisonous air, 46 

Microscope as detective, 265, -66 

Milk, 262, 263, 264, 266 

Mineral oils, 237 

Mineral waters, 104 

Mixtures and compounds, 33, 77 

Moissan, 54, 198, 200 

Molecules, 36, 48 

Mortar, 93 

N 

Naphtha, 135, 144, 283 

Native elements, 31 

Natural gas, 136 

Nitrates in the soil, 222 

Nitre in gunpowder, 171 

Nitric acid from the atmosphere, 

202, 224, 249 
Nitro-explosives, 174 
Nitrogen, 42 
Nitrogen for plants, 22 1 
Nitrogen iodide, 166 



Nitro-glycerine, 177, 336, 337 
Nobel, 336, 337 
Noble metals, 68 
Non-electrolytes, 311 



Oils, 237 

Oil wells, 134 

Ores, 62 

Organic substances, 29, 250 

Osmotic pressure, 305, 306, 307 

Oxygen, 42, 58, 96, 336 

Oxygen from air, 190, 195 

Oxyhydrogen flame, 197 

Ozone, 58 



Paint, 241 

Palm oil, 242 

Paper duty, 276 

Paracelsus, 27 

Paraffin oil, 149 

Paste, 55 

Peas, 228 

Peat, 131, 139, 149 

Perkin, Sir William, 285, 286, 287 

Petrifying springs, 100 

Petroleum, 135 

Pharaoh's serpent, 250 

Phenacetine, 288 

Philosopher's stone, 24 

Phosphorescent sulphides, 329, 

330 
Phosphorus, 51 
Phosphorus from bones, 201 
Phosphorus in matches, 122 
Photomicrographs, 325 
Pig-iron, 63 
Pins, 73 

Plant chemistry, 219 
Platinum, 68, 125, 196, 331, 332 
Platinum solution, 332, 333 



346 



INDEX 



Polluted water. 

i. 90 

Potatoes. - 
Priuce R 
Prussian blue, 281 



Quickliir 



Radium, ft! 

Ramsay, Sir Williai. 
Rapidity of exploit i 178 
Rate of crysta 
Rayleigh, Loni 
Red pbosphoru 
Refining of copper. 

Refrigeration. 
Regenerative burner, 160 
Respirating apparatus, 89 
Respiration, 1 

fe en rays, 323 
Rubidiun. 
Rubies, I 



Saccharine. 2S- 
Safety lamp, 163 
8afety matches 
Salt and now, L81 
Salt-cake 
Saltpttrr. 171 
Salt sol. 



Baj phi 

L01 

I 
. _m;» 
3 
Slag, 871, - 

Slag wool, 

Dg of lime, 92. 

1 7 1 

Ehnol 

. L81 

Soda indv 

.Solar spectrum, 210, 81 1 
I :>on dioxi . > 

Specific gi, 

- 

L'as mole 

- 

Stalactite-. LOO 
LOO 

of flame. 

.i^AT hOlllt'.' 

1 - \ 
Hum coal 



INDEX 



Sulphuric acid, 231, 232, 233, 235, 

281, 330 
Sulphur springs, 105 
Super-cooling, 317 
Superphosphate, 225 
Supersaturated solutions, 315 
Sympathetic inks, 320 
Synthesis, 248 
Synthetic camphor, 256 



Tallow dips, 244 

Tantalum, 70 

Tar, 147 

Thermit, 67 

Thoria, 328, 329 

Tinder, 120 

Tinplate, 73, 117 

Transmutation of metals, 24 

Treacle, 230 

Tungsten, 71 

Turpentine, 256 



U 



Urea, 250 



Vacuum by liquid hydrogen, 191 
Vacuum vessels, 187, 188 
Vinegar, 86 
Virgin soil, 223 
• Vitriol, 85 
Volta's cell, 291 

W 

Washing soda, 320 

Water, 95-105 

Water as catalytic agent, 327 

Water gas, 151 

Water in milk, 263 

Water of crystallisation, 318, 319 

Wheat meal, 227 

Wohler, 250, 251, 253 

Wood, 131, 139 

Wood charcoal, 57, 143 

Wrought-iron, 63 



Yellow phosphorus, 51 

z 

Zero, absolute, 191 



9** 



THE END 



Printed by Ballantyne, Hanson & Co 
Edinburgh <&■= London. 







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s* \*G < y o * v * A O ''. 






